diff --git a/solver/mates/__init__.py b/solver/mates/__init__.py
index e2b66ad..fa8a5d5 100644
--- a/solver/mates/__init__.py
+++ b/solver/mates/__init__.py
@@ -1,5 +1,10 @@
 """Mate-level constraint types for assembly analysis."""
 
+from solver.mates.conversion import (
+    MateAnalysisResult,
+    analyze_mate_assembly,
+    convert_mates_to_joints,
+)
 from solver.mates.patterns import (
     JointPattern,
     PatternMatch,
@@ -18,8 +23,11 @@ __all__ = [
     "GeometryType",
     "JointPattern",
     "Mate",
+    "MateAnalysisResult",
     "MateType",
     "PatternMatch",
+    "analyze_mate_assembly",
+    "convert_mates_to_joints",
     "dof_removed",
     "recognize_patterns",
 ]
diff --git a/solver/mates/conversion.py b/solver/mates/conversion.py
new file mode 100644
index 0000000..c8016ba
--- /dev/null
+++ b/solver/mates/conversion.py
@@ -0,0 +1,276 @@
+"""Mate-to-joint conversion and assembly analysis.
+
+Bridges the mate-level constraint representation to the existing
+joint-based analysis pipeline. Converts recognized mate patterns
+to Joint objects, then runs the pebble game and Jacobian analysis,
+maintaining bidirectional traceability between mates and joints.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import TYPE_CHECKING
+
+import numpy as np
+
+from solver.datagen.labeling import AssemblyLabels, label_assembly
+from solver.datagen.types import (
+    ConstraintAnalysis,
+    Joint,
+    JointType,
+    RigidBody,
+)
+from solver.mates.patterns import PatternMatch, recognize_patterns
+
+if TYPE_CHECKING:
+    from typing import Any
+
+    from solver.mates.primitives import Mate
+
+__all__ = [
+    "MateAnalysisResult",
+    "analyze_mate_assembly",
+    "convert_mates_to_joints",
+]
+
+
+# ---------------------------------------------------------------------------
+# Result dataclass
+# ---------------------------------------------------------------------------
+
+
+@dataclass
+class MateAnalysisResult:
+    """Combined result of mate-based assembly analysis.
+
+    Attributes:
+        patterns: Recognized joint patterns from mate grouping.
+        joints: Joint objects produced by conversion.
+        mate_to_joint: Mapping from mate_id to list of joint_ids.
+        joint_to_mates: Mapping from joint_id to list of mate_ids.
+        analysis: Constraint analysis from pebble game + Jacobian.
+        labels: Full ground truth labels from label_assembly.
+    """
+
+    patterns: list[PatternMatch]
+    joints: list[Joint]
+    mate_to_joint: dict[int, list[int]] = field(default_factory=dict)
+    joint_to_mates: dict[int, list[int]] = field(default_factory=dict)
+    analysis: ConstraintAnalysis | None = None
+    labels: AssemblyLabels | None = None
+
+    def to_dict(self) -> dict[str, Any]:
+        """Return a JSON-serializable dict."""
+        return {
+            "patterns": [p.to_dict() for p in self.patterns],
+            "joints": [
+                {
+                    "joint_id": j.joint_id,
+                    "body_a": j.body_a,
+                    "body_b": j.body_b,
+                    "joint_type": j.joint_type.name,
+                }
+                for j in self.joints
+            ],
+            "mate_to_joint": self.mate_to_joint,
+            "joint_to_mates": self.joint_to_mates,
+            "labels": self.labels.to_dict() if self.labels else None,
+        }
+
+
+# ---------------------------------------------------------------------------
+# Pattern-to-JointType mapping
+# ---------------------------------------------------------------------------
+
+# Maps (JointPattern value) to JointType for known patterns.
+# Used by convert_mates_to_joints when a full pattern is recognized.
+_PATTERN_JOINT_MAP: dict[str, JointType] = {
+    "hinge": JointType.REVOLUTE,
+    "slider": JointType.SLIDER,
+    "cylinder": JointType.CYLINDRICAL,
+    "ball": JointType.BALL,
+    "planar": JointType.PLANAR,
+    "fixed": JointType.FIXED,
+}
+
+# Fallback mapping for individual mate types when no pattern is recognized.
+_MATE_JOINT_FALLBACK: dict[str, JointType] = {
+    "COINCIDENT": JointType.PLANAR,
+    "CONCENTRIC": JointType.CYLINDRICAL,
+    "PARALLEL": JointType.PARALLEL,
+    "PERPENDICULAR": JointType.PERPENDICULAR,
+    "TANGENT": JointType.DISTANCE,
+    "DISTANCE": JointType.DISTANCE,
+    "ANGLE": JointType.PERPENDICULAR,
+    "LOCK": JointType.FIXED,
+}
+
+
+# ---------------------------------------------------------------------------
+# Conversion
+# ---------------------------------------------------------------------------
+
+
+def _compute_joint_params(
+    pattern: PatternMatch,
+) -> tuple[np.ndarray, np.ndarray, np.ndarray]:
+    """Extract anchor and axis from pattern mates.
+
+    Returns:
+        (anchor_a, anchor_b, axis)
+    """
+    anchor_a = np.zeros(3)
+    anchor_b = np.zeros(3)
+    axis = np.array([0.0, 0.0, 1.0])
+
+    for mate in pattern.mates:
+        ref_a = mate.ref_a
+        ref_b = mate.ref_b
+        anchor_a = ref_a.origin.copy()
+        anchor_b = ref_b.origin.copy()
+        if ref_a.direction is not None:
+            axis = ref_a.direction.copy()
+            break
+
+    return anchor_a, anchor_b, axis
+
+
+def _convert_single_mate(
+    mate: Mate,
+    joint_id: int,
+) -> Joint:
+    """Convert a single unmatched mate to a Joint."""
+    joint_type = _MATE_JOINT_FALLBACK.get(mate.mate_type.name, JointType.DISTANCE)
+
+    anchor_a = mate.ref_a.origin.copy()
+    anchor_b = mate.ref_b.origin.copy()
+    axis = np.array([0.0, 0.0, 1.0])
+    if mate.ref_a.direction is not None:
+        axis = mate.ref_a.direction.copy()
+
+    return Joint(
+        joint_id=joint_id,
+        body_a=mate.ref_a.body_id,
+        body_b=mate.ref_b.body_id,
+        joint_type=joint_type,
+        anchor_a=anchor_a,
+        anchor_b=anchor_b,
+        axis=axis,
+    )
+
+
+def convert_mates_to_joints(
+    mates: list[Mate],
+    bodies: list[RigidBody] | None = None,
+) -> tuple[list[Joint], dict[int, list[int]], dict[int, list[int]]]:
+    """Convert mates to Joint objects via pattern recognition.
+
+    For each body pair:
+    - If mates form a recognized pattern, emit the equivalent joint.
+    - Otherwise, emit individual joints for each unmatched mate.
+
+    Args:
+        mates: Mate constraints to convert.
+        bodies: Optional body list (unused currently, reserved for
+            future geometry lookups).
+
+    Returns:
+        (joints, mate_to_joint, joint_to_mates) tuple.
+    """
+    if not mates:
+        return [], {}, {}
+
+    patterns = recognize_patterns(mates)
+    joints: list[Joint] = []
+    mate_to_joint: dict[int, list[int]] = {}
+    joint_to_mates: dict[int, list[int]] = {}
+
+    # Track which mates have been consumed by full-confidence patterns
+    consumed_mate_ids: set[int] = set()
+    next_joint_id = 0
+
+    # First pass: emit joints for full-confidence patterns
+    for pattern in patterns:
+        if pattern.confidence < 1.0:
+            continue
+        if pattern.pattern.value not in _PATTERN_JOINT_MAP:
+            continue
+
+        # Check if any of these mates were already consumed
+        mate_ids = [m.mate_id for m in pattern.mates]
+        if any(mid in consumed_mate_ids for mid in mate_ids):
+            continue
+
+        joint_type = _PATTERN_JOINT_MAP[pattern.pattern.value]
+        anchor_a, anchor_b, axis = _compute_joint_params(pattern)
+
+        joint = Joint(
+            joint_id=next_joint_id,
+            body_a=pattern.body_a,
+            body_b=pattern.body_b,
+            joint_type=joint_type,
+            anchor_a=anchor_a,
+            anchor_b=anchor_b,
+            axis=axis,
+        )
+        joints.append(joint)
+
+        joint_to_mates[next_joint_id] = mate_ids
+        for mid in mate_ids:
+            mate_to_joint.setdefault(mid, []).append(next_joint_id)
+            consumed_mate_ids.add(mid)
+
+        next_joint_id += 1
+
+    # Second pass: emit individual joints for unconsumed mates
+    for mate in mates:
+        if mate.mate_id in consumed_mate_ids:
+            continue
+
+        joint = _convert_single_mate(mate, next_joint_id)
+        joints.append(joint)
+
+        joint_to_mates[next_joint_id] = [mate.mate_id]
+        mate_to_joint.setdefault(mate.mate_id, []).append(next_joint_id)
+
+        next_joint_id += 1
+
+    return joints, mate_to_joint, joint_to_mates
+
+
+# ---------------------------------------------------------------------------
+# Full analysis pipeline
+# ---------------------------------------------------------------------------
+
+
+def analyze_mate_assembly(
+    bodies: list[RigidBody],
+    mates: list[Mate],
+    ground_body: int | None = None,
+) -> MateAnalysisResult:
+    """Run the full analysis pipeline on a mate-based assembly.
+
+    Orchestrates: recognize_patterns -> convert_mates_to_joints ->
+    label_assembly, returning a combined result with full traceability.
+
+    Args:
+        bodies: Rigid bodies in the assembly.
+        mates: Mate constraints between the bodies.
+        ground_body: If set, this body is fixed to the world.
+
+    Returns:
+        MateAnalysisResult with patterns, joints, mappings, and labels.
+    """
+    patterns = recognize_patterns(mates)
+    joints, mate_to_joint, joint_to_mates = convert_mates_to_joints(mates, bodies)
+
+    labels = label_assembly(bodies, joints, ground_body)
+
+    return MateAnalysisResult(
+        patterns=patterns,
+        joints=joints,
+        mate_to_joint=mate_to_joint,
+        joint_to_mates=joint_to_mates,
+        analysis=labels.analysis,
+        labels=labels,
+    )
diff --git a/tests/mates/test_conversion.py b/tests/mates/test_conversion.py
new file mode 100644
index 0000000..b2740ca
--- /dev/null
+++ b/tests/mates/test_conversion.py
@@ -0,0 +1,287 @@
+"""Tests for solver.mates.conversion -- mate-to-joint conversion."""
+
+from __future__ import annotations
+
+import numpy as np
+
+from solver.datagen.types import JointType, RigidBody
+from solver.mates.conversion import (
+    MateAnalysisResult,
+    analyze_mate_assembly,
+    convert_mates_to_joints,
+)
+from solver.mates.primitives import GeometryRef, GeometryType, Mate, MateType
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _make_ref(
+    body_id: int,
+    geom_type: GeometryType,
+    *,
+    origin: np.ndarray | None = None,
+    direction: np.ndarray | None = None,
+) -> GeometryRef:
+    """Factory for GeometryRef with sensible defaults."""
+    if origin is None:
+        origin = np.zeros(3)
+    if direction is None and geom_type in {
+        GeometryType.FACE,
+        GeometryType.AXIS,
+        GeometryType.PLANE,
+    }:
+        direction = np.array([0.0, 0.0, 1.0])
+    return GeometryRef(
+        body_id=body_id,
+        geometry_type=geom_type,
+        geometry_id="Geom001",
+        origin=origin,
+        direction=direction,
+    )
+
+
+def _make_bodies(n: int) -> list[RigidBody]:
+    """Create n bodies at distinct positions."""
+    return [RigidBody(body_id=i, position=np.array([float(i), 0.0, 0.0])) for i in range(n)]
+
+
+# ---------------------------------------------------------------------------
+# convert_mates_to_joints
+# ---------------------------------------------------------------------------
+
+
+class TestConvertMatesToJoints:
+    """convert_mates_to_joints function."""
+
+    def test_empty_input(self) -> None:
+        joints, m2j, j2m = convert_mates_to_joints([])
+        assert joints == []
+        assert m2j == {}
+        assert j2m == {}
+
+    def test_hinge_pattern(self) -> None:
+        """Concentric + Coincident(plane) -> single REVOLUTE joint."""
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.CONCENTRIC,
+                ref_a=_make_ref(0, GeometryType.AXIS),
+                ref_b=_make_ref(1, GeometryType.AXIS),
+            ),
+            Mate(
+                mate_id=1,
+                mate_type=MateType.COINCIDENT,
+                ref_a=_make_ref(0, GeometryType.PLANE),
+                ref_b=_make_ref(1, GeometryType.PLANE),
+            ),
+        ]
+        joints, m2j, j2m = convert_mates_to_joints(mates)
+        assert len(joints) == 1
+        assert joints[0].joint_type is JointType.REVOLUTE
+        assert joints[0].body_a == 0
+        assert joints[0].body_b == 1
+        # Both mates map to the single joint
+        assert 0 in m2j
+        assert 1 in m2j
+        assert j2m[joints[0].joint_id] == [0, 1]
+
+    def test_lock_pattern(self) -> None:
+        """Lock -> FIXED joint."""
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+        ]
+        joints, _m2j, _j2m = convert_mates_to_joints(mates)
+        assert len(joints) == 1
+        assert joints[0].joint_type is JointType.FIXED
+
+    def test_unmatched_mate_fallback(self) -> None:
+        """A single ANGLE mate with no pattern -> individual joint."""
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.ANGLE,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+        ]
+        joints, _m2j, _j2m = convert_mates_to_joints(mates)
+        assert len(joints) == 1
+        assert joints[0].joint_type is JointType.PERPENDICULAR
+
+    def test_mapping_consistency(self) -> None:
+        """mate_to_joint and joint_to_mates are consistent."""
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.CONCENTRIC,
+                ref_a=_make_ref(0, GeometryType.AXIS),
+                ref_b=_make_ref(1, GeometryType.AXIS),
+            ),
+            Mate(
+                mate_id=1,
+                mate_type=MateType.COINCIDENT,
+                ref_a=_make_ref(0, GeometryType.PLANE),
+                ref_b=_make_ref(1, GeometryType.PLANE),
+            ),
+            Mate(
+                mate_id=2,
+                mate_type=MateType.DISTANCE,
+                ref_a=_make_ref(2, GeometryType.POINT),
+                ref_b=_make_ref(3, GeometryType.POINT),
+            ),
+        ]
+        joints, m2j, j2m = convert_mates_to_joints(mates)
+        # Every mate should be in m2j
+        for mate in mates:
+            assert mate.mate_id in m2j
+        # Every joint should be in j2m
+        for joint in joints:
+            assert joint.joint_id in j2m
+
+    def test_joint_axis_from_geometry(self) -> None:
+        """Joint axis should come from mate geometry direction."""
+        axis_dir = np.array([1.0, 0.0, 0.0])
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.CONCENTRIC,
+                ref_a=_make_ref(0, GeometryType.AXIS, direction=axis_dir),
+                ref_b=_make_ref(1, GeometryType.AXIS, direction=axis_dir),
+            ),
+            Mate(
+                mate_id=1,
+                mate_type=MateType.COINCIDENT,
+                ref_a=_make_ref(0, GeometryType.PLANE),
+                ref_b=_make_ref(1, GeometryType.PLANE),
+            ),
+        ]
+        joints, _, _ = convert_mates_to_joints(mates)
+        np.testing.assert_array_almost_equal(joints[0].axis, axis_dir)
+
+
+# ---------------------------------------------------------------------------
+# MateAnalysisResult
+# ---------------------------------------------------------------------------
+
+
+class TestMateAnalysisResult:
+    """MateAnalysisResult dataclass."""
+
+    def test_to_dict(self) -> None:
+        result = MateAnalysisResult(
+            patterns=[],
+            joints=[],
+        )
+        d = result.to_dict()
+        assert d["patterns"] == []
+        assert d["joints"] == []
+        assert d["labels"] is None
+
+
+# ---------------------------------------------------------------------------
+# analyze_mate_assembly
+# ---------------------------------------------------------------------------
+
+
+class TestAnalyzeMateAssembly:
+    """Full pipeline: mates -> joints -> analysis."""
+
+    def test_two_bodies_hinge(self) -> None:
+        """Two bodies connected by hinge mates -> underconstrained (1 DOF)."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.CONCENTRIC,
+                ref_a=_make_ref(0, GeometryType.AXIS),
+                ref_b=_make_ref(1, GeometryType.AXIS),
+            ),
+            Mate(
+                mate_id=1,
+                mate_type=MateType.COINCIDENT,
+                ref_a=_make_ref(0, GeometryType.PLANE),
+                ref_b=_make_ref(1, GeometryType.PLANE),
+            ),
+        ]
+        result = analyze_mate_assembly(bodies, mates)
+        assert result.analysis is not None
+        assert result.labels is not None
+        # A revolute joint removes 5 DOF, leaving 1 internal DOF
+        assert result.analysis.combinatorial_internal_dof == 1
+        assert len(result.joints) == 1
+        assert result.joints[0].joint_type is JointType.REVOLUTE
+
+    def test_two_bodies_fixed(self) -> None:
+        """Two bodies with lock mate -> well-constrained."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+        ]
+        result = analyze_mate_assembly(bodies, mates)
+        assert result.analysis is not None
+        assert result.analysis.combinatorial_internal_dof == 0
+        assert result.analysis.is_rigid
+
+    def test_grounded_assembly(self) -> None:
+        """Grounded assembly analysis works."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+        ]
+        result = analyze_mate_assembly(bodies, mates, ground_body=0)
+        assert result.analysis is not None
+        assert result.analysis.is_rigid
+
+    def test_no_mates(self) -> None:
+        """Assembly with no mates should be fully underconstrained."""
+        bodies = _make_bodies(2)
+        result = analyze_mate_assembly(bodies, [])
+        assert result.analysis is not None
+        assert result.analysis.combinatorial_internal_dof == 6
+        assert len(result.joints) == 0
+
+    def test_single_body(self) -> None:
+        """Single body, no mates."""
+        bodies = _make_bodies(1)
+        result = analyze_mate_assembly(bodies, [])
+        assert result.analysis is not None
+        assert len(result.joints) == 0
+
+    def test_result_traceability(self) -> None:
+        """mate_to_joint and joint_to_mates populated in result."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.CONCENTRIC,
+                ref_a=_make_ref(0, GeometryType.AXIS),
+                ref_b=_make_ref(1, GeometryType.AXIS),
+            ),
+            Mate(
+                mate_id=1,
+                mate_type=MateType.COINCIDENT,
+                ref_a=_make_ref(0, GeometryType.PLANE),
+                ref_b=_make_ref(1, GeometryType.PLANE),
+            ),
+        ]
+        result = analyze_mate_assembly(bodies, mates)
+        assert 0 in result.mate_to_joint
+        assert 1 in result.mate_to_joint
+        assert len(result.joint_to_mates) > 0