diff --git a/src/resolve/validate.rs b/src/resolve/validate.rs
index 750c624..388a341 100644
--- a/src/resolve/validate.rs
+++ b/src/resolve/validate.rs
@@ -542,6 +542,133 @@ pub fn validate_species_type_invariance(file: &File, collector: &mut ErrorCollec
     }
 }
 
+/// Validate concept_comparison patterns against the concept registry
+///
+/// Checks:
+/// 1. The concept_comparison name references an existing concept
+/// 2. All variant names in patterns exist in the concept's enum sub-concepts
+/// 3. Patterns are exhaustive (all variants are covered)
+pub fn validate_concept_comparison_patterns(
+    file: &File,
+    registry: &crate::resolve::types::ConceptRegistry,
+    collector: &mut ErrorCollector,
+) {
+    for decl in &file.declarations {
+        if let Declaration::ConceptComparison(comp) = decl {
+            // Check that the concept exists
+            let concept = match registry.lookup_concept(&comp.name) {
+                | Some(c) => c,
+                | None => {
+                    collector.add(ResolveError::ValidationError {
+                        message: format!(
+                            "Concept '{}' not found for concept_comparison",
+                            comp.name
+                        ),
+                        help: Some(format!(
+                            "Add 'concept {}' before defining a concept_comparison for it.",
+                            comp.name
+                        )),
+                    });
+                    continue;
+                },
+            };
+
+            // Collect all enum variants from all enum sub-concepts
+            let mut all_variants: HashSet<String> = HashSet::new();
+            for sc_info in concept.sub_concepts.values() {
+                if let SubConceptKind::Enum { variants } = &sc_info.kind {
+                    for variant in variants {
+                        all_variants.insert(variant.clone());
+                    }
+                }
+            }
+
+            // Check each variant pattern references valid variants
+            let mut covered_variants: HashSet<String> = HashSet::new();
+            for pattern in &comp.variants {
+                // Check that the variant name is a known variant
+                if !all_variants.contains(&pattern.name) {
+                    collector.add(ResolveError::ValidationError {
+                        message: format!(
+                            "Variant '{}' not found in concept '{}'",
+                            pattern.name, comp.name
+                        ),
+                        help: Some(format!(
+                            "Available variants for '{}': {}",
+                            comp.name,
+                            if all_variants.is_empty() {
+                                "(none - add sub_concept with enum variants)".to_string()
+                            } else {
+                                let mut sorted: Vec<_> = all_variants.iter().collect();
+                                sorted.sort();
+                                sorted
+                                    .iter()
+                                    .map(|s| s.as_str())
+                                    .collect::<Vec<_>>()
+                                    .join(", ")
+                            }
+                        )),
+                    });
+                } else {
+                    covered_variants.insert(pattern.name.clone());
+                }
+
+                // Check field conditions reference valid fields in the Is values
+                for condition in &pattern.conditions {
+                    if let Condition::Is(values) = &condition.condition {
+                        for value in values {
+                            // Check that the value references a valid variant
+                            if !all_variants.contains(value) {
+                                collector.add(ResolveError::ValidationError {
+                                    message: format!(
+                                        "Value '{}' in condition for variant '{}' not found in concept '{}'",
+                                        value, pattern.name, comp.name
+                                    ),
+                                    help: Some(format!(
+                                        "Available variants: {}",
+                                        {
+                                            let mut sorted: Vec<_> = all_variants.iter().collect();
+                                            sorted.sort();
+                                            sorted.iter().map(|s| s.as_str()).collect::<Vec<_>>().join(", ")
+                                        }
+                                    )),
+                                });
+                            }
+                        }
+                    }
+                }
+            }
+
+            // Check exhaustiveness - all variants should be covered
+            let uncovered: Vec<_> = all_variants.difference(&covered_variants).collect();
+            if !uncovered.is_empty() {
+                let mut sorted: Vec<_> = uncovered.into_iter().collect();
+                sorted.sort();
+                collector.add(ResolveError::ValidationError {
+                    message: format!(
+                        "concept_comparison '{}' is not exhaustive: missing variants {}",
+                        comp.name,
+                        sorted
+                            .iter()
+                            .map(|s| format!("'{}'", s))
+                            .collect::<Vec<_>>()
+                            .join(", ")
+                    ),
+                    help: Some(format!(
+                        "Add patterns for all variants of concept '{}'. Missing: {}",
+                        comp.name,
+                        sorted
+                            .iter()
+                            .map(|s| s.as_str())
+                            .collect::<Vec<_>>()
+                            .join(", ")
+                    )),
+                });
+            }
+        }
+    }
+}
+
 /// Validate an entire file
 ///
 /// Collects all validation errors and returns them together instead of failing
@@ -552,6 +679,8 @@ pub fn validate_file(file: &File, action_registry: &HashSet<String>) -> Result<(
     // Type system validation
     validate_sub_concept_parents(file, &mut collector);
     validate_species_type_invariance(file, &mut collector);
+    let concept_registry = crate::resolve::types::ConceptRegistry::from_file(file);
+    validate_concept_comparison_patterns(file, &concept_registry, &mut collector);
 
     for decl in &file.declarations {
         match decl {
@@ -1053,4 +1182,179 @@ mod tests {
         validate_species_type_invariance(&file, &mut collector);
         assert!(!collector.has_errors());
     }
+
+    // ===== Concept Comparison Validation Tests =====
+
+    use crate::resolve::types::ConceptRegistry;
+
+    fn make_concept_comparison_file() -> File {
+        File {
+            declarations: vec![
+                Declaration::Concept(ConceptDecl {
+                    name: "Cup".to_string(),
+                    span: Span::new(0, 10),
+                }),
+                Declaration::SubConcept(SubConceptDecl {
+                    name: "Type".to_string(),
+                    parent_concept: "Cup".to_string(),
+                    kind: SubConceptKind::Enum {
+                        variants: vec![
+                            "Small".to_string(),
+                            "Medium".to_string(),
+                            "Large".to_string(),
+                        ],
+                    },
+                    span: Span::new(20, 60),
+                }),
+            ],
+        }
+    }
+
+    #[test]
+    fn test_concept_comparison_valid_exhaustive() {
+        let mut file = make_concept_comparison_file();
+        file.declarations
+            .push(Declaration::ConceptComparison(ConceptComparisonDecl {
+                name: "Cup".to_string(),
+                variants: vec![
+                    VariantPattern {
+                        name: "Small".to_string(),
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                    VariantPattern {
+                        name: "Medium".to_string(),
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                    VariantPattern {
+                        name: "Large".to_string(),
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                ],
+                span: Span::new(0, 100),
+            }));
+
+        let registry = ConceptRegistry::from_file(&file);
+        let mut collector = ErrorCollector::new();
+        validate_concept_comparison_patterns(&file, &registry, &mut collector);
+        assert!(!collector.has_errors());
+    }
+
+    #[test]
+    fn test_concept_comparison_not_exhaustive() {
+        let mut file = make_concept_comparison_file();
+        file.declarations
+            .push(Declaration::ConceptComparison(ConceptComparisonDecl {
+                name: "Cup".to_string(),
+                variants: vec![
+                    VariantPattern {
+                        name: "Small".to_string(),
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                    // Missing Medium and Large
+                ],
+                span: Span::new(0, 100),
+            }));
+
+        let registry = ConceptRegistry::from_file(&file);
+        let mut collector = ErrorCollector::new();
+        validate_concept_comparison_patterns(&file, &registry, &mut collector);
+        assert!(collector.has_errors());
+    }
+
+    #[test]
+    fn test_concept_comparison_unknown_variant() {
+        let mut file = make_concept_comparison_file();
+        file.declarations
+            .push(Declaration::ConceptComparison(ConceptComparisonDecl {
+                name: "Cup".to_string(),
+                variants: vec![
+                    VariantPattern {
+                        name: "Small".to_string(),
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                    VariantPattern {
+                        name: "Medium".to_string(),
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                    VariantPattern {
+                        name: "Large".to_string(),
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                    VariantPattern {
+                        name: "Huge".to_string(), // Not a valid variant
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                ],
+                span: Span::new(0, 100),
+            }));
+
+        let registry = ConceptRegistry::from_file(&file);
+        let mut collector = ErrorCollector::new();
+        validate_concept_comparison_patterns(&file, &registry, &mut collector);
+        assert!(collector.has_errors());
+    }
+
+    #[test]
+    fn test_concept_comparison_missing_concept() {
+        let file = File {
+            declarations: vec![Declaration::ConceptComparison(ConceptComparisonDecl {
+                name: "NonExistent".to_string(),
+                variants: vec![],
+                span: Span::new(0, 100),
+            })],
+        };
+
+        let registry = ConceptRegistry::from_file(&file);
+        let mut collector = ErrorCollector::new();
+        validate_concept_comparison_patterns(&file, &registry, &mut collector);
+        assert!(collector.has_errors());
+    }
+
+    #[test]
+    fn test_concept_comparison_with_field_conditions() {
+        let mut file = make_concept_comparison_file();
+        file.declarations
+            .push(Declaration::ConceptComparison(ConceptComparisonDecl {
+                name: "Cup".to_string(),
+                variants: vec![
+                    VariantPattern {
+                        name: "Small".to_string(),
+                        conditions: vec![FieldCondition {
+                            field_name: "material".to_string(),
+                            condition: Condition::Is(vec!["Medium".to_string()]), // Valid variant ref
+                            span: Span::new(0, 10),
+                        }],
+                        span: Span::new(0, 10),
+                    },
+                    VariantPattern {
+                        name: "Medium".to_string(),
+                        conditions: vec![FieldCondition {
+                            field_name: "material".to_string(),
+                            condition: Condition::Any,
+                            span: Span::new(0, 10),
+                        }],
+                        span: Span::new(0, 10),
+                    },
+                    VariantPattern {
+                        name: "Large".to_string(),
+                        conditions: vec![],
+                        span: Span::new(0, 10),
+                    },
+                ],
+                span: Span::new(0, 100),
+            }));
+
+        let registry = ConceptRegistry::from_file(&file);
+        let mut collector = ErrorCollector::new();
+        validate_concept_comparison_patterns(&file, &registry, &mut collector);
+        assert!(!collector.has_errors());
+    }
 }