diff --git a/wfe-yaml/src/lib.rs b/wfe-yaml/src/lib.rs
index e094058..28a3234 100644
--- a/wfe-yaml/src/lib.rs
+++ b/wfe-yaml/src/lib.rs
@@ -3,6 +3,7 @@ pub mod error;
 pub mod executors;
 pub mod interpolation;
 pub mod schema;
+pub mod types;
 pub mod validation;
 
 use std::collections::HashMap;
@@ -10,29 +11,78 @@ use std::collections::HashMap;
 use crate::compiler::CompiledWorkflow;
 use crate::error::YamlWorkflowError;
 
-/// Load a workflow from a YAML file path, applying variable interpolation.
+/// Load workflows from a YAML file path, applying variable interpolation.
+/// Returns a Vec of compiled workflows (supports multi-workflow files).
 pub fn load_workflow(
     path: &std::path::Path,
     config: &HashMap<String, serde_json::Value>,
 ) -> Result<CompiledWorkflow, YamlWorkflowError> {
     let yaml = std::fs::read_to_string(path)?;
-    load_workflow_from_str(&yaml, config)
+    load_single_workflow_from_str(&yaml, config)
 }
 
-/// Load a workflow from a YAML string, applying variable interpolation.
+/// Load workflows from a YAML string, applying variable interpolation.
+/// Returns a Vec of compiled workflows (supports multi-workflow files).
 pub fn load_workflow_from_str(
     yaml: &str,
     config: &HashMap<String, serde_json::Value>,
-) -> Result<CompiledWorkflow, YamlWorkflowError> {
+) -> Result<Vec<CompiledWorkflow>, YamlWorkflowError> {
     // Interpolate variables.
     let interpolated = interpolation::interpolate(yaml, config)?;
 
-    // Parse YAML.
-    let workflow: schema::YamlWorkflow = serde_yaml::from_str(&interpolated)?;
+    // Parse YAML as multi-workflow file.
+    let file: schema::YamlWorkflowFile = serde_yaml::from_str(&interpolated)?;
 
-    // Validate.
-    validation::validate(&workflow.workflow)?;
+    let specs = resolve_workflow_specs(file)?;
 
-    // Compile.
-    compiler::compile(&workflow.workflow)
+    // Validate (multi-workflow validation includes per-workflow + cross-references).
+    validation::validate_multi(&specs)?;
+
+    // Compile each workflow.
+    let mut results = Vec::with_capacity(specs.len());
+    for spec in &specs {
+        results.push(compiler::compile(spec)?);
+    }
+
+    Ok(results)
+}
+
+/// Load a single workflow from a YAML string. Returns an error if the file
+/// contains more than one workflow. This is a backward-compatible convenience
+/// function.
+pub fn load_single_workflow_from_str(
+    yaml: &str,
+    config: &HashMap<String, serde_json::Value>,
+) -> Result<CompiledWorkflow, YamlWorkflowError> {
+    let mut workflows = load_workflow_from_str(yaml, config)?;
+    if workflows.len() != 1 {
+        return Err(YamlWorkflowError::Validation(format!(
+            "Expected single workflow, got {}",
+            workflows.len()
+        )));
+    }
+    Ok(workflows.remove(0))
+}
+
+/// Resolve a YamlWorkflowFile into a list of WorkflowSpecs.
+fn resolve_workflow_specs(
+    file: schema::YamlWorkflowFile,
+) -> Result<Vec<schema::WorkflowSpec>, YamlWorkflowError> {
+    match (file.workflow, file.workflows) {
+        (Some(single), None) => Ok(vec![single]),
+        (None, Some(multi)) => {
+            if multi.is_empty() {
+                return Err(YamlWorkflowError::Validation(
+                    "workflows list is empty".to_string(),
+                ));
+            }
+            Ok(multi)
+        }
+        (Some(_), Some(_)) => Err(YamlWorkflowError::Validation(
+            "Cannot specify both 'workflow' and 'workflows' in the same file".to_string(),
+        )),
+        (None, None) => Err(YamlWorkflowError::Validation(
+            "Must specify either 'workflow' or 'workflows'".to_string(),
+        )),
+    }
 }
diff --git a/wfe-yaml/src/schema.rs b/wfe-yaml/src/schema.rs
index db3835e..8005c44 100644
--- a/wfe-yaml/src/schema.rs
+++ b/wfe-yaml/src/schema.rs
@@ -2,6 +2,17 @@ use std::collections::HashMap;
 
 use serde::Deserialize;
 
+/// Top-level YAML file structure supporting both single and multi-workflow files.
+#[derive(Debug, Deserialize)]
+pub struct YamlWorkflowFile {
+    /// Single workflow (backward compatible).
+    pub workflow: Option<WorkflowSpec>,
+    /// Multiple workflows in one file.
+    pub workflows: Option<Vec<WorkflowSpec>>,
+}
+
+/// Legacy single-workflow top-level structure. Kept for backward compatibility
+/// with code that deserializes `YamlWorkflow` directly.
 #[derive(Debug, Deserialize)]
 pub struct YamlWorkflow {
     pub workflow: WorkflowSpec,
@@ -16,6 +27,13 @@ pub struct WorkflowSpec {
     #[serde(default)]
     pub error_behavior: Option<YamlErrorBehavior>,
     pub steps: Vec<YamlStep>,
+    /// Typed input schema: { field_name: type_string }.
+    /// Example: `"repo_url": "string"`, `"tags": "list<string>"`.
+    #[serde(default)]
+    pub inputs: HashMap<String, String>,
+    /// Typed output schema: { field_name: type_string }.
+    #[serde(default)]
+    pub outputs: HashMap<String, String>,
     /// Allow unknown top-level keys (e.g. `_templates`) for YAML anchors.
     #[serde(flatten)]
     pub _extra: HashMap<String, serde_yaml::Value>,
@@ -90,6 +108,13 @@ pub struct StepConfig {
     pub containerd_addr: Option<String>,
     /// CLI binary name for containerd steps: "nerdctl" (default) or "docker".
     pub cli: Option<String>,
+    // Workflow (sub-workflow) fields
+    /// Child workflow ID (for `type: workflow` steps).
+    #[serde(rename = "workflow")]
+    pub child_workflow: Option<String>,
+    /// Child workflow version (for `type: workflow` steps).
+    #[serde(rename = "workflow_version")]
+    pub child_version: Option<u32>,
 }
 
 /// YAML-level permission configuration for Deno steps.
diff --git a/wfe-yaml/src/types.rs b/wfe-yaml/src/types.rs
new file mode 100644
index 0000000..67a1e53
--- /dev/null
+++ b/wfe-yaml/src/types.rs
@@ -0,0 +1,252 @@
+/// Parsed type representation for workflow input/output schemas.
+///
+/// This mirrors what wfe-core's `SchemaType` will provide, but is self-contained
+/// so wfe-yaml can parse type strings without depending on wfe-core's schema module.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SchemaType {
+    String,
+    Number,
+    Integer,
+    Bool,
+    Any,
+    Optional(Box<SchemaType>),
+    List(Box<SchemaType>),
+    Map(Box<SchemaType>),
+}
+
+impl std::fmt::Display for SchemaType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            SchemaType::String => write!(f, "string"),
+            SchemaType::Number => write!(f, "number"),
+            SchemaType::Integer => write!(f, "integer"),
+            SchemaType::Bool => write!(f, "bool"),
+            SchemaType::Any => write!(f, "any"),
+            SchemaType::Optional(inner) => write!(f, "{inner}?"),
+            SchemaType::List(inner) => write!(f, "list<{inner}>"),
+            SchemaType::Map(inner) => write!(f, "map<{inner}>"),
+        }
+    }
+}
+
+/// Parse a type string like `"string"`, `"string?"`, `"list<number>"`, `"map<string>"`.
+///
+/// Supports:
+/// - Primitives: `"string"`, `"number"`, `"integer"`, `"bool"`, `"any"`
+/// - Optional: `"string?"` -> `Optional(String)`
+/// - List: `"list<string>"` -> `List(String)`
+/// - Map: `"map<number>"` -> `Map(Number)`
+/// - Nested generics: `"list<list<string>>"` -> `List(List(String))`
+pub fn parse_type_string(s: &str) -> Result<SchemaType, String> {
+    let s = s.trim();
+    if s.is_empty() {
+        return Err("Empty type string".to_string());
+    }
+
+    // Check for optional suffix (but not inside generics).
+    if s.ends_with('?') && !s.ends_with(">?") {
+        // Simple optional like "string?"
+        let inner = parse_type_string(&s[..s.len() - 1])?;
+        return Ok(SchemaType::Optional(Box::new(inner)));
+    }
+
+    // Handle optional on generic types like "list<string>?"
+    if s.ends_with(">?") {
+        let inner = parse_type_string(&s[..s.len() - 1])?;
+        return Ok(SchemaType::Optional(Box::new(inner)));
+    }
+
+    // Check for generic types: list<...> or map<...>
+    if let Some(inner_start) = s.find('<') {
+        if !s.ends_with('>') {
+            return Err(format!("Malformed generic type: '{s}' (missing closing '>')"));
+        }
+        let container = &s[..inner_start];
+        let inner_str = &s[inner_start + 1..s.len() - 1];
+
+        let inner_type = parse_type_string(inner_str)?;
+
+        match container {
+            "list" => Ok(SchemaType::List(Box::new(inner_type))),
+            "map" => Ok(SchemaType::Map(Box::new(inner_type))),
+            other => Err(format!("Unknown generic type: '{other}'")),
+        }
+    } else {
+        // Primitive types.
+        match s {
+            "string" => Ok(SchemaType::String),
+            "number" => Ok(SchemaType::Number),
+            "integer" => Ok(SchemaType::Integer),
+            "bool" => Ok(SchemaType::Bool),
+            "any" => Ok(SchemaType::Any),
+            other => Err(format!("Unknown type: '{other}'")),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_primitive_string() {
+        assert_eq!(parse_type_string("string").unwrap(), SchemaType::String);
+    }
+
+    #[test]
+    fn parse_primitive_number() {
+        assert_eq!(parse_type_string("number").unwrap(), SchemaType::Number);
+    }
+
+    #[test]
+    fn parse_primitive_integer() {
+        assert_eq!(parse_type_string("integer").unwrap(), SchemaType::Integer);
+    }
+
+    #[test]
+    fn parse_primitive_bool() {
+        assert_eq!(parse_type_string("bool").unwrap(), SchemaType::Bool);
+    }
+
+    #[test]
+    fn parse_primitive_any() {
+        assert_eq!(parse_type_string("any").unwrap(), SchemaType::Any);
+    }
+
+    #[test]
+    fn parse_optional_string() {
+        assert_eq!(
+            parse_type_string("string?").unwrap(),
+            SchemaType::Optional(Box::new(SchemaType::String))
+        );
+    }
+
+    #[test]
+    fn parse_optional_number() {
+        assert_eq!(
+            parse_type_string("number?").unwrap(),
+            SchemaType::Optional(Box::new(SchemaType::Number))
+        );
+    }
+
+    #[test]
+    fn parse_list_string() {
+        assert_eq!(
+            parse_type_string("list<string>").unwrap(),
+            SchemaType::List(Box::new(SchemaType::String))
+        );
+    }
+
+    #[test]
+    fn parse_map_number() {
+        assert_eq!(
+            parse_type_string("map<number>").unwrap(),
+            SchemaType::Map(Box::new(SchemaType::Number))
+        );
+    }
+
+    #[test]
+    fn parse_nested_list() {
+        assert_eq!(
+            parse_type_string("list<list<string>>").unwrap(),
+            SchemaType::List(Box::new(SchemaType::List(Box::new(SchemaType::String))))
+        );
+    }
+
+    #[test]
+    fn parse_nested_map_in_list() {
+        assert_eq!(
+            parse_type_string("list<map<integer>>").unwrap(),
+            SchemaType::List(Box::new(SchemaType::Map(Box::new(SchemaType::Integer))))
+        );
+    }
+
+    #[test]
+    fn parse_optional_list() {
+        assert_eq!(
+            parse_type_string("list<string>?").unwrap(),
+            SchemaType::Optional(Box::new(SchemaType::List(Box::new(SchemaType::String))))
+        );
+    }
+
+    #[test]
+    fn parse_unknown_type_error() {
+        let result = parse_type_string("foobar");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("Unknown type"));
+    }
+
+    #[test]
+    fn parse_unknown_generic_error() {
+        let result = parse_type_string("set<string>");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("Unknown generic type"));
+    }
+
+    #[test]
+    fn parse_empty_string_error() {
+        let result = parse_type_string("");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("Empty type string"));
+    }
+
+    #[test]
+    fn parse_malformed_generic_error() {
+        let result = parse_type_string("list<string");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("Malformed generic type"));
+    }
+
+    #[test]
+    fn parse_whitespace_trimmed() {
+        assert_eq!(parse_type_string("  string  ").unwrap(), SchemaType::String);
+    }
+
+    #[test]
+    fn parse_deeply_nested() {
+        assert_eq!(
+            parse_type_string("list<list<list<bool>>>").unwrap(),
+            SchemaType::List(Box::new(SchemaType::List(Box::new(SchemaType::List(
+                Box::new(SchemaType::Bool)
+            )))))
+        );
+    }
+
+    #[test]
+    fn display_roundtrip_primitives() {
+        for type_str in &["string", "number", "integer", "bool", "any"] {
+            let parsed = parse_type_string(type_str).unwrap();
+            assert_eq!(parsed.to_string(), *type_str);
+        }
+    }
+
+    #[test]
+    fn display_roundtrip_generics() {
+        for type_str in &["list<string>", "map<number>", "list<list<string>>"] {
+            let parsed = parse_type_string(type_str).unwrap();
+            assert_eq!(parsed.to_string(), *type_str);
+        }
+    }
+
+    #[test]
+    fn display_optional() {
+        let t = SchemaType::Optional(Box::new(SchemaType::String));
+        assert_eq!(t.to_string(), "string?");
+    }
+
+    #[test]
+    fn parse_map_any() {
+        assert_eq!(
+            parse_type_string("map<any>").unwrap(),
+            SchemaType::Map(Box::new(SchemaType::Any))
+        );
+    }
+
+    #[test]
+    fn parse_optional_bool() {
+        assert_eq!(
+            parse_type_string("bool?").unwrap(),
+            SchemaType::Optional(Box::new(SchemaType::Bool))
+        );
+    }
+}
diff --git a/wfe-yaml/tests/schema.rs b/wfe-yaml/tests/schema.rs
index f329fb1..dfdc371 100644
--- a/wfe-yaml/tests/schema.rs
+++ b/wfe-yaml/tests/schema.rs
@@ -1,4 +1,4 @@
-use wfe_yaml::schema::YamlWorkflow;
+use wfe_yaml::schema::{YamlWorkflow, YamlWorkflowFile};
 
 #[test]
 fn parse_minimal_yaml() {
@@ -192,3 +192,153 @@ workflow:
     assert_eq!(parsed.workflow.id, "template-wf");
     assert_eq!(parsed.workflow.steps.len(), 1);
 }
+
+// --- Multi-workflow file tests ---
+
+#[test]
+fn parse_single_workflow_file() {
+    let yaml = r#"
+workflow:
+  id: single
+  version: 1
+  steps:
+    - name: step1
+      type: shell
+      config:
+        run: echo hello
+"#;
+    let parsed: YamlWorkflowFile = serde_yaml::from_str(yaml).unwrap();
+    assert!(parsed.workflow.is_some());
+    assert!(parsed.workflows.is_none());
+    assert_eq!(parsed.workflow.unwrap().id, "single");
+}
+
+#[test]
+fn parse_multi_workflow_file() {
+    let yaml = r#"
+workflows:
+  - id: build-wf
+    version: 1
+    steps:
+      - name: build
+        type: shell
+        config:
+          run: cargo build
+  - id: test-wf
+    version: 1
+    steps:
+      - name: test
+        type: shell
+        config:
+          run: cargo test
+"#;
+    let parsed: YamlWorkflowFile = serde_yaml::from_str(yaml).unwrap();
+    assert!(parsed.workflow.is_none());
+    assert!(parsed.workflows.is_some());
+    let workflows = parsed.workflows.unwrap();
+    assert_eq!(workflows.len(), 2);
+    assert_eq!(workflows[0].id, "build-wf");
+    assert_eq!(workflows[1].id, "test-wf");
+}
+
+#[test]
+fn parse_workflow_with_input_output_schemas() {
+    let yaml = r#"
+workflow:
+  id: typed-wf
+  version: 1
+  inputs:
+    repo_url: string
+    tags: "list<string>"
+    verbose: bool?
+  outputs:
+    artifact_path: string
+    exit_code: integer
+  steps:
+    - name: step1
+      type: shell
+      config:
+        run: echo hello
+"#;
+    let parsed: YamlWorkflow = serde_yaml::from_str(yaml).unwrap();
+    assert_eq!(parsed.workflow.inputs.len(), 3);
+    assert_eq!(parsed.workflow.inputs.get("repo_url").unwrap(), "string");
+    assert_eq!(
+        parsed.workflow.inputs.get("tags").unwrap(),
+        "list<string>"
+    );
+    assert_eq!(parsed.workflow.inputs.get("verbose").unwrap(), "bool?");
+    assert_eq!(parsed.workflow.outputs.len(), 2);
+    assert_eq!(
+        parsed.workflow.outputs.get("artifact_path").unwrap(),
+        "string"
+    );
+    assert_eq!(
+        parsed.workflow.outputs.get("exit_code").unwrap(),
+        "integer"
+    );
+}
+
+#[test]
+fn parse_step_with_workflow_type() {
+    let yaml = r#"
+workflow:
+  id: parent-wf
+  version: 1
+  steps:
+    - name: run-child
+      type: workflow
+      config:
+        workflow: child-wf
+        workflow_version: 2
+      inputs:
+        - name: repo_url
+          path: data.repo
+      outputs:
+        - name: result
+"#;
+    let parsed: YamlWorkflow = serde_yaml::from_str(yaml).unwrap();
+    let step = &parsed.workflow.steps[0];
+    assert_eq!(step.step_type.as_deref(), Some("workflow"));
+    let config = step.config.as_ref().unwrap();
+    assert_eq!(config.child_workflow.as_deref(), Some("child-wf"));
+    assert_eq!(config.child_version, Some(2));
+    assert_eq!(step.inputs.len(), 1);
+    assert_eq!(step.outputs.len(), 1);
+}
+
+#[test]
+fn parse_workflow_step_version_defaults() {
+    let yaml = r#"
+workflow:
+  id: parent-wf
+  version: 1
+  steps:
+    - name: run-child
+      type: workflow
+      config:
+        workflow: child-wf
+"#;
+    let parsed: YamlWorkflow = serde_yaml::from_str(yaml).unwrap();
+    let config = parsed.workflow.steps[0].config.as_ref().unwrap();
+    assert_eq!(config.child_workflow.as_deref(), Some("child-wf"));
+    // version not specified, should be None in schema (compiler defaults to 1).
+    assert_eq!(config.child_version, None);
+}
+
+#[test]
+fn parse_empty_inputs_outputs_default() {
+    let yaml = r#"
+workflow:
+  id: no-schema-wf
+  version: 1
+  steps:
+    - name: step1
+      type: shell
+      config:
+        run: echo hello
+"#;
+    let parsed: YamlWorkflow = serde_yaml::from_str(yaml).unwrap();
+    assert!(parsed.workflow.inputs.is_empty());
+    assert!(parsed.workflow.outputs.is_empty());
+}
diff --git a/wfe-yaml/tests/types.rs b/wfe-yaml/tests/types.rs
new file mode 100644
index 0000000..bf36031
--- /dev/null
+++ b/wfe-yaml/tests/types.rs
@@ -0,0 +1,107 @@
+use wfe_yaml::types::{parse_type_string, SchemaType};
+
+#[test]
+fn parse_all_primitives() {
+    assert_eq!(parse_type_string("string").unwrap(), SchemaType::String);
+    assert_eq!(parse_type_string("number").unwrap(), SchemaType::Number);
+    assert_eq!(parse_type_string("integer").unwrap(), SchemaType::Integer);
+    assert_eq!(parse_type_string("bool").unwrap(), SchemaType::Bool);
+    assert_eq!(parse_type_string("any").unwrap(), SchemaType::Any);
+}
+
+#[test]
+fn parse_optional_types() {
+    assert_eq!(
+        parse_type_string("string?").unwrap(),
+        SchemaType::Optional(Box::new(SchemaType::String))
+    );
+    assert_eq!(
+        parse_type_string("integer?").unwrap(),
+        SchemaType::Optional(Box::new(SchemaType::Integer))
+    );
+}
+
+#[test]
+fn parse_list_types() {
+    assert_eq!(
+        parse_type_string("list<string>").unwrap(),
+        SchemaType::List(Box::new(SchemaType::String))
+    );
+    assert_eq!(
+        parse_type_string("list<number>").unwrap(),
+        SchemaType::List(Box::new(SchemaType::Number))
+    );
+}
+
+#[test]
+fn parse_map_types() {
+    assert_eq!(
+        parse_type_string("map<string>").unwrap(),
+        SchemaType::Map(Box::new(SchemaType::String))
+    );
+    assert_eq!(
+        parse_type_string("map<any>").unwrap(),
+        SchemaType::Map(Box::new(SchemaType::Any))
+    );
+}
+
+#[test]
+fn parse_nested_generics() {
+    assert_eq!(
+        parse_type_string("list<list<string>>").unwrap(),
+        SchemaType::List(Box::new(SchemaType::List(Box::new(SchemaType::String))))
+    );
+    assert_eq!(
+        parse_type_string("map<list<integer>>").unwrap(),
+        SchemaType::Map(Box::new(SchemaType::List(Box::new(SchemaType::Integer))))
+    );
+}
+
+#[test]
+fn parse_optional_generic() {
+    assert_eq!(
+        parse_type_string("list<string>?").unwrap(),
+        SchemaType::Optional(Box::new(SchemaType::List(Box::new(SchemaType::String))))
+    );
+}
+
+#[test]
+fn parse_unknown_type_returns_error() {
+    let err = parse_type_string("foobar").unwrap_err();
+    assert!(err.contains("Unknown type"), "Got: {err}");
+}
+
+#[test]
+fn parse_unknown_generic_container_returns_error() {
+    let err = parse_type_string("set<string>").unwrap_err();
+    assert!(err.contains("Unknown generic type"), "Got: {err}");
+}
+
+#[test]
+fn parse_empty_returns_error() {
+    let err = parse_type_string("").unwrap_err();
+    assert!(err.contains("Empty"), "Got: {err}");
+}
+
+#[test]
+fn parse_malformed_generic_returns_error() {
+    let err = parse_type_string("list<string").unwrap_err();
+    assert!(err.contains("Malformed"), "Got: {err}");
+}
+
+#[test]
+fn display_roundtrip() {
+    for s in &[
+        "string",
+        "number",
+        "integer",
+        "bool",
+        "any",
+        "list<string>",
+        "map<number>",
+        "list<list<string>>",
+    ] {
+        let parsed = parse_type_string(s).unwrap();
+        assert_eq!(parsed.to_string(), *s, "Roundtrip failed for {s}");
+    }
+}