diff --git a/wfe-opensearch/Cargo.toml b/wfe-opensearch/Cargo.toml
new file mode 100644
index 0000000..61ef731
--- /dev/null
+++ b/wfe-opensearch/Cargo.toml
@@ -0,0 +1,25 @@
+[package]
+name = "wfe-opensearch"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+description = "OpenSearch index provider for WFE"
+
+[dependencies]
+wfe-core = { workspace = true }
+opensearch = { workspace = true }
+tokio = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }
+async-trait = { workspace = true }
+thiserror = { workspace = true }
+tracing = { workspace = true }
+
+[dev-dependencies]
+wfe-core = { workspace = true, features = ["test-support"] }
+pretty_assertions = { workspace = true }
+rstest = { workspace = true }
+tokio = { workspace = true, features = ["test-util"] }
+uuid = { workspace = true }
+chrono = { workspace = true }
+opensearch = { workspace = true }
diff --git a/wfe-opensearch/src/lib.rs b/wfe-opensearch/src/lib.rs
new file mode 100644
index 0000000..463dbb8
--- /dev/null
+++ b/wfe-opensearch/src/lib.rs
@@ -0,0 +1,296 @@
+use async_trait::async_trait;
+use opensearch::http::transport::Transport;
+use opensearch::{IndexParts, OpenSearch, SearchParts};
+use serde::{Deserialize, Serialize};
+use serde_json::json;
+use tracing::debug;
+use wfe_core::models::{WorkflowInstance, WorkflowStatus};
+use wfe_core::traits::search::{Page, SearchFilter, SearchIndex, WorkflowSearchResult};
+
+/// Document structure stored in OpenSearch.
+#[derive(Debug, Serialize, Deserialize)]
+struct WorkflowDocument {
+    id: String,
+    workflow_definition_id: String,
+    version: u32,
+    status: String,
+    reference: Option<String>,
+    description: Option<String>,
+    data: serde_json::Value,
+    create_time: String,
+    complete_time: Option<String>,
+}
+
+impl From<&WorkflowInstance> for WorkflowDocument {
+    fn from(instance: &WorkflowInstance) -> Self {
+        Self {
+            id: instance.id.clone(),
+            workflow_definition_id: instance.workflow_definition_id.clone(),
+            version: instance.version,
+            status: serde_json::to_value(instance.status)
+                .ok()
+                .and_then(|v| v.as_str().map(String::from))
+                .unwrap_or_default(),
+            reference: instance.reference.clone(),
+            description: instance.description.clone(),
+            data: instance.data.clone(),
+            create_time: instance.create_time.to_rfc3339(),
+            complete_time: instance.complete_time.map(|t| t.to_rfc3339()),
+        }
+    }
+}
+
+/// OpenSearch-backed search index for workflow instances.
+pub struct OpenSearchIndex {
+    client: OpenSearch,
+    index_name: String,
+}
+
+impl OpenSearchIndex {
+    /// Create a new OpenSearch index provider.
+    ///
+    /// # Arguments
+    /// * `url` - OpenSearch server URL (e.g. `http://localhost:9200`)
+    /// * `index_name` - Name of the index to use
+    pub fn new(url: &str, index_name: &str) -> wfe_core::Result<Self> {
+        let transport = Transport::single_node(url)
+            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send + Sync>)?;
+        let client = OpenSearch::new(transport);
+        Ok(Self {
+            client,
+            index_name: index_name.to_string(),
+        })
+    }
+
+    /// Get a reference to the underlying OpenSearch client (useful for tests).
+    pub fn client(&self) -> &OpenSearch {
+        &self.client
+    }
+
+    /// Get the index name.
+    pub fn index_name(&self) -> &str {
+        &self.index_name
+    }
+}
+
+#[async_trait]
+impl SearchIndex for OpenSearchIndex {
+    async fn start(&self) -> wfe_core::Result<()> {
+        let exists = self
+            .client
+            .indices()
+            .exists(opensearch::indices::IndicesExistsParts::Index(&[
+                &self.index_name,
+            ]))
+            .send()
+            .await
+            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send + Sync>)?;
+
+        if exists.status_code().is_success() {
+            debug!(index = %self.index_name, "Index already exists");
+            return Ok(());
+        }
+
+        let body = json!({
+            "mappings": {
+                "properties": {
+                    "id": { "type": "keyword" },
+                    "workflow_definition_id": { "type": "keyword" },
+                    "version": { "type": "integer" },
+                    "status": { "type": "keyword" },
+                    "reference": { "type": "keyword" },
+                    "description": { "type": "text" },
+                    "data": { "type": "object", "enabled": false },
+                    "create_time": { "type": "date" },
+                    "complete_time": { "type": "date" }
+                }
+            }
+        });
+
+        let response = self
+            .client
+            .indices()
+            .create(opensearch::indices::IndicesCreateParts::Index(
+                &self.index_name,
+            ))
+            .body(body)
+            .send()
+            .await
+            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send + Sync>)?;
+
+        if !response.status_code().is_success() {
+            let text = response
+                .text()
+                .await
+                .unwrap_or_else(|_| "unknown error".to_string());
+            return Err(wfe_core::WfeError::Persistence(format!(
+                "Failed to create index: {text}"
+            )));
+        }
+
+        debug!(index = %self.index_name, "Index created");
+        Ok(())
+    }
+
+    async fn stop(&self) -> wfe_core::Result<()> {
+        Ok(())
+    }
+
+    async fn index_workflow(&self, instance: &WorkflowInstance) -> wfe_core::Result<()> {
+        let doc = WorkflowDocument::from(instance);
+
+        let response = self
+            .client
+            .index(IndexParts::IndexId(&self.index_name, &doc.id))
+            .body(serde_json::to_value(&doc)?)
+            .send()
+            .await
+            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send + Sync>)?;
+
+        if !response.status_code().is_success() {
+            let text = response
+                .text()
+                .await
+                .unwrap_or_else(|_| "unknown error".to_string());
+            return Err(wfe_core::WfeError::Persistence(format!(
+                "Failed to index workflow: {text}"
+            )));
+        }
+
+        debug!(id = %instance.id, index = %self.index_name, "Workflow indexed");
+        Ok(())
+    }
+
+    async fn search(
+        &self,
+        terms: &str,
+        skip: u64,
+        take: u64,
+        filters: &[SearchFilter],
+    ) -> wfe_core::Result<Page<WorkflowSearchResult>> {
+        let mut must_clauses: Vec<serde_json::Value> = Vec::new();
+        let mut filter_clauses: Vec<serde_json::Value> = Vec::new();
+
+        if !terms.is_empty() {
+            must_clauses.push(json!({
+                "multi_match": {
+                    "query": terms,
+                    "fields": ["description", "reference", "workflow_definition_id"]
+                }
+            }));
+        }
+
+        for filter in filters {
+            match filter {
+                SearchFilter::Status(status) => {
+                    let status_str = serde_json::to_value(status)
+                        .ok()
+                        .and_then(|v| v.as_str().map(String::from))
+                        .unwrap_or_default();
+                    filter_clauses.push(json!({
+                        "term": { "status": status_str }
+                    }));
+                }
+                SearchFilter::DateRange {
+                    field,
+                    before,
+                    after,
+                } => {
+                    let mut range = serde_json::Map::new();
+                    if let Some(before) = before {
+                        range.insert("lt".to_string(), json!(before.to_rfc3339()));
+                    }
+                    if let Some(after) = after {
+                        range.insert("gte".to_string(), json!(after.to_rfc3339()));
+                    }
+                    if !range.is_empty() {
+                        filter_clauses.push(json!({
+                            "range": { field.clone(): range }
+                        }));
+                    }
+                }
+                SearchFilter::Reference(reference) => {
+                    filter_clauses.push(json!({
+                        "term": { "reference": reference }
+                    }));
+                }
+            }
+        }
+
+        let query = if must_clauses.is_empty() && filter_clauses.is_empty() {
+            json!({ "match_all": {} })
+        } else {
+            let mut bool_query = serde_json::Map::new();
+            if !must_clauses.is_empty() {
+                bool_query.insert("must".to_string(), json!(must_clauses));
+            }
+            if !filter_clauses.is_empty() {
+                bool_query.insert("filter".to_string(), json!(filter_clauses));
+            }
+            json!({ "bool": bool_query })
+        };
+
+        let body = json!({
+            "query": query,
+            "from": skip,
+            "size": take,
+        });
+
+        let response = self
+            .client
+            .search(SearchParts::Index(&[&self.index_name]))
+            .body(body)
+            .send()
+            .await
+            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send + Sync>)?;
+
+        if !response.status_code().is_success() {
+            let text = response
+                .text()
+                .await
+                .unwrap_or_else(|_| "unknown error".to_string());
+            return Err(wfe_core::WfeError::Persistence(format!(
+                "Search failed: {text}"
+            )));
+        }
+
+        let response_body: serde_json::Value = response
+            .json()
+            .await
+            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send + Sync>)?;
+
+        let total = response_body["hits"]["total"]["value"]
+            .as_u64()
+            .unwrap_or(0);
+
+        let hits = response_body["hits"]["hits"]
+            .as_array()
+            .cloned()
+            .unwrap_or_default();
+
+        let mut results = Vec::with_capacity(hits.len());
+        for hit in &hits {
+            let source = &hit["_source"];
+            let status_str = source["status"].as_str().unwrap_or("Runnable");
+            let status: WorkflowStatus =
+                serde_json::from_value(json!(status_str)).unwrap_or_default();
+
+            results.push(WorkflowSearchResult {
+                id: source["id"].as_str().unwrap_or_default().to_string(),
+                workflow_definition_id: source["workflow_definition_id"]
+                    .as_str()
+                    .unwrap_or_default()
+                    .to_string(),
+                version: source["version"].as_u64().unwrap_or(0) as u32,
+                status,
+                reference: source["reference"].as_str().map(String::from),
+                description: source["description"].as_str().map(String::from),
+            });
+        }
+
+        Ok(Page {
+            data: results,
+            total,
+        })
+    }
+}
diff --git a/wfe-opensearch/tests/search.rs b/wfe-opensearch/tests/search.rs
new file mode 100644
index 0000000..038e9e9
--- /dev/null
+++ b/wfe-opensearch/tests/search.rs
@@ -0,0 +1,198 @@
+use chrono::Utc;
+use opensearch::http::transport::Transport;
+use opensearch::OpenSearch;
+use pretty_assertions::assert_eq;
+use serde_json::json;
+use uuid::Uuid;
+use wfe_core::models::{WorkflowInstance, WorkflowStatus};
+use wfe_core::traits::search::{SearchFilter, SearchIndex};
+use wfe_opensearch::OpenSearchIndex;
+
+const OPENSEARCH_URL: &str = "http://localhost:9200";
+
+/// Check if OpenSearch is reachable, skip test if not.
+async fn opensearch_available() -> bool {
+    let transport = Transport::single_node(OPENSEARCH_URL);
+    if transport.is_err() {
+        return false;
+    }
+    let client = OpenSearch::new(transport.unwrap());
+    client
+        .ping()
+        .send()
+        .await
+        .map(|r| r.status_code().is_success())
+        .unwrap_or(false)
+}
+
+/// Helper to create a unique test index and return the provider + cleanup handle.
+async fn setup() -> Option<(OpenSearchIndex, String)> {
+    if !opensearch_available().await {
+        eprintln!("OpenSearch not available, skipping test");
+        return None;
+    }
+    let index_name = format!("wfe_test_{}", Uuid::new_v4());
+    let provider = OpenSearchIndex::new(OPENSEARCH_URL, &index_name).unwrap();
+    provider.start().await.unwrap();
+    Some((provider, index_name))
+}
+
+/// Refresh the index so documents become searchable immediately.
+async fn refresh_index(provider: &OpenSearchIndex) {
+    let url = format!("/{}/_refresh", provider.index_name());
+    provider
+        .client()
+        .send(
+            opensearch::http::Method::Post,
+            &url,
+            opensearch::http::headers::HeaderMap::new(),
+            Option::<&serde_json::Value>::None,
+            Some(b"".as_ref()),
+            None,
+        )
+        .await
+        .unwrap();
+}
+
+/// Delete the test index.
+async fn cleanup(provider: &OpenSearchIndex) {
+    let _ = provider
+        .client()
+        .indices()
+        .delete(opensearch::indices::IndicesDeleteParts::Index(&[
+            provider.index_name(),
+        ]))
+        .send()
+        .await;
+}
+
+fn make_instance(description: Option<&str>, reference: Option<&str>) -> WorkflowInstance {
+    let mut instance = WorkflowInstance::new("test-workflow", 1, json!({"key": "value"}));
+    instance.description = description.map(String::from);
+    instance.reference = reference.map(String::from);
+    instance
+}
+
+#[tokio::test]
+async fn index_and_search_by_terms() {
+    let Some((provider, _index)) = setup().await else {
+        return;
+    };
+
+    let instance = make_instance(Some("Process the quarterly financial report"), None);
+    provider.index_workflow(&instance).await.unwrap();
+    refresh_index(&provider).await;
+
+    let page = provider
+        .search("quarterly financial", 0, 10, &[])
+        .await
+        .unwrap();
+
+    assert_eq!(page.total, 1);
+    assert_eq!(page.data.len(), 1);
+    assert_eq!(page.data[0].id, instance.id);
+    assert_eq!(
+        page.data[0].description.as_deref(),
+        Some("Process the quarterly financial report")
+    );
+
+    cleanup(&provider).await;
+}
+
+#[tokio::test]
+async fn search_with_status_filter() {
+    let Some((provider, _index)) = setup().await else {
+        return;
+    };
+
+    let mut runnable = make_instance(Some("Runnable workflow"), None);
+    runnable.status = WorkflowStatus::Runnable;
+
+    let mut complete = make_instance(Some("Complete workflow"), None);
+    complete.status = WorkflowStatus::Complete;
+    complete.complete_time = Some(Utc::now());
+
+    provider.index_workflow(&runnable).await.unwrap();
+    provider.index_workflow(&complete).await.unwrap();
+    refresh_index(&provider).await;
+
+    let page = provider
+        .search("", 0, 10, &[SearchFilter::Status(WorkflowStatus::Complete)])
+        .await
+        .unwrap();
+
+    assert_eq!(page.total, 1);
+    assert_eq!(page.data[0].id, complete.id);
+    assert_eq!(page.data[0].status, WorkflowStatus::Complete);
+
+    cleanup(&provider).await;
+}
+
+#[tokio::test]
+async fn search_with_no_results() {
+    let Some((provider, _index)) = setup().await else {
+        return;
+    };
+
+    let instance = make_instance(Some("A regular workflow"), None);
+    provider.index_workflow(&instance).await.unwrap();
+    refresh_index(&provider).await;
+
+    let page = provider
+        .search("nonexistent-xyzzy-42", 0, 10, &[])
+        .await
+        .unwrap();
+
+    assert_eq!(page.total, 0);
+    assert!(page.data.is_empty());
+
+    cleanup(&provider).await;
+}
+
+#[tokio::test]
+async fn index_multiple_and_paginate() {
+    let Some((provider, _index)) = setup().await else {
+        return;
+    };
+
+    let mut instances = Vec::new();
+    for i in 0..5 {
+        let instance = make_instance(Some(&format!("Paginated workflow number {i}")), None);
+        provider.index_workflow(&instance).await.unwrap();
+        instances.push(instance);
+    }
+    refresh_index(&provider).await;
+
+    // Search all, but skip 2 and take 2
+    let page = provider.search("Paginated workflow", 2, 2, &[]).await.unwrap();
+
+    assert_eq!(page.total, 5);
+    assert_eq!(page.data.len(), 2);
+
+    cleanup(&provider).await;
+}
+
+#[tokio::test]
+async fn search_by_reference() {
+    let Some((provider, _index)) = setup().await else {
+        return;
+    };
+
+    let inst1 = make_instance(Some("First workflow"), Some("REF-001"));
+    let inst2 = make_instance(Some("Second workflow"), Some("REF-002"));
+
+    provider.index_workflow(&inst1).await.unwrap();
+    provider.index_workflow(&inst2).await.unwrap();
+    refresh_index(&provider).await;
+
+    let page = provider
+        .search("", 0, 10, &[SearchFilter::Reference("REF-001".to_string())])
+        .await
+        .unwrap();
+
+    assert_eq!(page.total, 1);
+    assert_eq!(page.data[0].id, inst1.id);
+    assert_eq!(page.data[0].reference.as_deref(), Some("REF-001"));
+
+    cleanup(&provider).await;
+}