diff --git a/src/lsp/code_actions.rs b/src/lsp/code_actions.rs
index d6b9ded..ce23e72 100644
--- a/src/lsp/code_actions.rs
+++ b/src/lsp/code_actions.rs
@@ -1704,6 +1704,9 @@ fn get_declaration_name(decl: &crate::syntax::ast::Declaration) -> String {
         | Declaration::Schedule(s) => s.name.clone(),
         | Declaration::Behavior(b) => b.name.clone(),
         | Declaration::Use(_) => "use".to_string(),
+        | Declaration::Concept(c) => c.name.clone(),
+        | Declaration::SubConcept(sc) => sc.name.clone(),
+        | Declaration::ConceptComparison(cc) => cc.name.clone(),
     }
 }
 
@@ -1722,6 +1725,9 @@ fn get_declaration_type_name(decl: &crate::syntax::ast::Declaration) -> &'static
         | Declaration::Schedule(_) => "Schedule",
         | Declaration::Behavior(_) => "Behavior",
         | Declaration::Use(_) => "Use",
+        | Declaration::Concept(_) => "Concept",
+        | Declaration::SubConcept(_) => "Sub Concept",
+        | Declaration::ConceptComparison(_) => "Concept Comparison",
     }
 }
 
@@ -1953,6 +1959,9 @@ fn get_declaration_span(decl: &crate::syntax::ast::Declaration) -> Span {
         | Declaration::Schedule(s) => s.span.clone(),
         | Declaration::Behavior(b) => b.span.clone(),
         | Declaration::Use(u) => u.span.clone(),
+        | Declaration::Concept(c) => c.span.clone(),
+        | Declaration::SubConcept(sc) => sc.span.clone(),
+        | Declaration::ConceptComparison(cc) => cc.span.clone(),
     }
 }
 
diff --git a/src/lsp/hover.rs b/src/lsp/hover.rs
index ee844d0..bac4344 100644
--- a/src/lsp/hover.rs
+++ b/src/lsp/hover.rs
@@ -179,6 +179,9 @@ fn get_declaration_name(decl: &Declaration) -> Option<String> {
         | Declaration::Schedule(s) => Some(s.name.clone()),
         | Declaration::Behavior(b) => Some(b.name.clone()),
         | Declaration::Use(_) => None,
+        | Declaration::Concept(_) |
+        Declaration::SubConcept(_) |
+        Declaration::ConceptComparison(_) => None, // TODO: Implement hover for type system
     }
 }
 
@@ -196,6 +199,9 @@ fn format_declaration_hover(decl: &Declaration, _kind: &DeclKind) -> Hover {
         | Declaration::Schedule(s) => format_schedule_hover(s),
         | Declaration::Behavior(b) => format_behavior_hover(b),
         | Declaration::Use(_) => "**use** declaration".to_string(),
+        | Declaration::Concept(_) => "**concept** declaration".to_string(),
+        | Declaration::SubConcept(_) => "**sub_concept** declaration".to_string(),
+        | Declaration::ConceptComparison(_) => "**concept_comparison** declaration".to_string(),
     };
 
     Hover {
diff --git a/src/lsp/semantic_tokens.rs b/src/lsp/semantic_tokens.rs
index 156b49d..ecf7f6a 100644
--- a/src/lsp/semantic_tokens.rs
+++ b/src/lsp/semantic_tokens.rs
@@ -407,6 +407,12 @@ pub fn get_semantic_tokens(doc: &Document) -> Option<SemanticTokensResult> {
                     }
                 }
             },
+            | Declaration::Concept(_) |
+            Declaration::SubConcept(_) |
+            Declaration::ConceptComparison(_) => {
+                // TODO: Implement semantic highlighting for type system
+                // declarations
+            },
         }
     }
 
diff --git a/src/lsp/symbols.rs b/src/lsp/symbols.rs
index 70dc4ff..f7b6192 100644
--- a/src/lsp/symbols.rs
+++ b/src/lsp/symbols.rs
@@ -96,6 +96,9 @@ fn extract_declaration_symbol(
             extract_variant_symbols(&e.variants, positions),
         ),
         | Declaration::Use(_) => return None, // Use statements don't create symbols
+        | Declaration::Concept(_) |
+        Declaration::SubConcept(_) |
+        Declaration::ConceptComparison(_) => return None, // TODO: Implement symbols for type system
     };
 
     let (start_line, start_col) = positions.offset_to_position(span.start);
diff --git a/src/resolve/convert.rs b/src/resolve/convert.rs
index 65b8e43..1066840 100644
--- a/src/resolve/convert.rs
+++ b/src/resolve/convert.rs
@@ -98,6 +98,11 @@ pub fn convert_file_with_all_files(
                 // Use declarations are handled during name resolution, not
                 // conversion
             },
+            | ast::Declaration::Concept(_) |
+            ast::Declaration::SubConcept(_) |
+            ast::Declaration::ConceptComparison(_) => {
+                // TODO: Implement conversion for type system declarations
+            },
         }
     }
 
diff --git a/src/resolve/names.rs b/src/resolve/names.rs
index 5fdb2e2..f38b1fd 100644
--- a/src/resolve/names.rs
+++ b/src/resolve/names.rs
@@ -139,6 +139,10 @@ impl NameTable {
                 | Declaration::Location(l) => (l.name.clone(), DeclKind::Location, l.span.clone()),
                 | Declaration::Species(s) => (s.name.clone(), DeclKind::Species, s.span.clone()),
                 | Declaration::Enum(e) => (e.name.clone(), DeclKind::Enum, e.span.clone()),
+                | Declaration::Concept(_) |
+                Declaration::SubConcept(_) |
+                Declaration::ConceptComparison(_) => continue, /* TODO: Implement name resolution
+                                                                * for type system */
             };
 
             // For now, qualified path is just the name
diff --git a/src/resolve/references.rs b/src/resolve/references.rs
index 0073bf8..969f4a5 100644
--- a/src/resolve/references.rs
+++ b/src/resolve/references.rs
@@ -191,6 +191,11 @@ fn find_references_in_declaration(
         | Declaration::Use(_) => {
             // Use statements are handled separately
         },
+        | Declaration::Concept(_) |
+        Declaration::SubConcept(_) |
+        Declaration::ConceptComparison(_) => {
+            // TODO: Implement reference finding for type system
+        },
     }
 
     refs
diff --git a/src/syntax/ast.rs b/src/syntax/ast.rs
index 83a9ffd..59648be 100644
--- a/src/syntax/ast.rs
+++ b/src/syntax/ast.rs
@@ -70,6 +70,9 @@ pub enum Declaration {
     Location(Location),
     Species(Species),
     Enum(EnumDecl),
+    Concept(ConceptDecl),
+    SubConcept(SubConceptDecl),
+    ConceptComparison(ConceptComparisonDecl),
 }
 
 /// Use statement for importing definitions
@@ -414,6 +417,46 @@ pub struct EnumDecl {
     pub span: Span,
 }
 
+/// Concept declaration - base type definition
+#[derive(Debug, Clone, PartialEq)]
+pub struct ConceptDecl {
+    pub name: String,
+    pub span: Span,
+}
+
+/// Sub-concept declaration - enum or record subtype
+#[derive(Debug, Clone, PartialEq)]
+pub struct SubConceptDecl {
+    pub name: String,
+    pub parent_concept: String,
+    pub kind: SubConceptKind,
+    pub span: Span,
+}
+
+/// Sub-concept can be either enum-like or record-like
+#[derive(Debug, Clone, PartialEq)]
+pub enum SubConceptKind {
+    Enum { variants: Vec<String> },
+    Record { fields: Vec<Field> },
+}
+
+/// Concept comparison - compile-time enum mapping between two concepts
+#[derive(Debug, Clone, PartialEq)]
+pub struct ConceptComparisonDecl {
+    pub name: String,
+    pub left_concept: String,
+    pub right_concept: String,
+    pub mappings: Vec<ConceptMapping>,
+    pub span: Span,
+}
+
+/// A single mapping entry in a concept comparison
+#[derive(Debug, Clone, PartialEq)]
+pub struct ConceptMapping {
+    pub left_variant: String,
+    pub right_variant: String,
+}
+
 /// Expression AST for conditions and queries
 #[derive(Debug, Clone, PartialEq)]
 pub enum Expr {