diff --git a/internal/mapper/BUILD.bazel b/internal/mapper/BUILD.bazel
index 5b988d0f..65bf5afd 100644
--- a/internal/mapper/BUILD.bazel
+++ b/internal/mapper/BUILD.bazel
@@ -4,6 +4,7 @@ go_library(
     name = "mapper",
     srcs = [
         "build_description.go",
+        "changed_targets.go",
         "errors.go",
         "target_graph.go",
     ],
diff --git a/internal/mapper/changed_targets.go b/internal/mapper/changed_targets.go
new file mode 100644
index 00000000..8b28d185
--- /dev/null
+++ b/internal/mapper/changed_targets.go
@@ -0,0 +1,40 @@
+package mapper
+
+import (
+	"github.com/uber/tango/entity"
+	"github.com/uber/tango/tangopb"
+)
+
+// ChangedTargetsResponseToProto converts an entity.GetChangedTargetsResponse
+// to its proto equivalent for gRPC streaming.
+func ChangedTargetsResponseToProto(resp *entity.GetChangedTargetsResponse) *tangopb.GetChangedTargetsResponse {
+	if resp.Metadata != nil {
+		return &tangopb.GetChangedTargetsResponse{
+			Item: &tangopb.GetChangedTargetsResponse_Metadata{
+				Metadata: metadataToProto(resp.Metadata),
+			},
+		}
+	}
+	changed := make([]*tangopb.ChangedTarget, len(resp.ChangedTargets))
+	for i := range resp.ChangedTargets {
+		ct := &resp.ChangedTargets[i]
+		changed[i] = &tangopb.ChangedTarget{
+			ChangeType: tangopb.ChangeType(int32(ct.ChangeType)),
+			OldTarget:  optionalTargetToProto(ct.OldTarget),
+			NewTarget:  optionalTargetToProto(ct.NewTarget),
+			Distance:   ct.Distance,
+		}
+	}
+	return &tangopb.GetChangedTargetsResponse{
+		Item: &tangopb.GetChangedTargetsResponse_ChangedTargets{
+			ChangedTargets: &tangopb.ChangedTargets{ChangedTargets: changed},
+		},
+	}
+}
+
+func optionalTargetToProto(t *entity.OptimizedTarget) *tangopb.OptimizedTarget {
+	if t == nil {
+		return nil
+	}
+	return optimizedTargetToProto(t)
+}
diff --git a/internal/mapper/target_graph.go b/internal/mapper/target_graph.go
index 45717d82..4ff3aa28 100644
--- a/internal/mapper/target_graph.go
+++ b/internal/mapper/target_graph.go
@@ -24,3 +24,48 @@ func ProtoToGetTargetGraphRequest(req *tangopb.GetTargetGraphRequest) (entity.Ge
 		BypassCache:       req.GetBypassCache(),
 	}, nil
 }
+
+// GetTargetGraphResponseToProto converts an entity.GetTargetGraphResponse to
+// the corresponding proto GetTargetGraphResponse.
+func GetTargetGraphResponseToProto(chunk *entity.GetTargetGraphResponse) *tangopb.GetTargetGraphResponse {
+	if chunk.Metadata != nil {
+		return &tangopb.GetTargetGraphResponse{
+			Item: &tangopb.GetTargetGraphResponse_Metadata{
+				Metadata: metadataToProto(chunk.Metadata),
+			},
+		}
+	}
+	targets := make([]*tangopb.OptimizedTarget, len(chunk.Targets))
+	for i := range chunk.Targets {
+		targets[i] = optimizedTargetToProto(&chunk.Targets[i])
+	}
+	return &tangopb.GetTargetGraphResponse{
+		Item: &tangopb.GetTargetGraphResponse_Targets{
+			Targets: &tangopb.OptimizedTargets{Targets: targets},
+		},
+	}
+}
+
+// metadataToProto converts an entity.Metadata to a proto Metadata.
+func metadataToProto(m *entity.Metadata) *tangopb.Metadata {
+	return &tangopb.Metadata{
+		TargetIdMapping:             m.TargetIDMapping,
+		RuleTypeMapping:             m.RuleTypeMapping,
+		TagMapping:                  m.TagMapping,
+		AttributeNameMapping:        m.AttributeNameMapping,
+		AttributeStringValueMapping: m.AttributeStringValueMapping,
+	}
+}
+
+func optimizedTargetToProto(t *entity.OptimizedTarget) *tangopb.OptimizedTarget {
+	return &tangopb.OptimizedTarget{
+		Id:                 t.ID,
+		Hash:               t.Hash,
+		DirectDependencies: t.DirectDependencies,
+		RuleType:           t.RuleType,
+		Tags:               t.Tags,
+		Root:               t.Root,
+		External:           t.External,
+		Attributes:         t.Attributes,
+	}
+}
diff --git a/internal/mapper/target_graph_test.go b/internal/mapper/target_graph_test.go
index 0d0d92fb..ebec3962 100644
--- a/internal/mapper/target_graph_test.go
+++ b/internal/mapper/target_graph_test.go
@@ -86,3 +86,41 @@ func TestProtoToGetTargetGraphRequest(t *testing.T) {
 		})
 	}
 }
+
+func TestGetTargetGraphResponseToProto_Targets(t *testing.T) {
+	t.Parallel()
+
+	chunk := entity.GetTargetGraphResponse{
+		Targets: []entity.OptimizedTarget{
+			{ID: 1, Hash: "ab", DirectDependencies: []int32{2}, RuleType: 10, Root: true},
+			{ID: 2, Hash: "cd", Tags: []int32{5, 6}, External: true},
+		},
+	}
+
+	proto := GetTargetGraphResponseToProto(&chunk)
+	targets := proto.GetItem().(*tangopb.GetTargetGraphResponse_Targets)
+	require.Len(t, targets.Targets.GetTargets(), 2)
+
+	got := targets.Targets.GetTargets()[0]
+	assert.Equal(t, int32(1), got.GetId())
+	assert.Equal(t, "ab", got.GetHash())
+	assert.Equal(t, []int32{2}, got.GetDirectDependencies())
+	assert.Equal(t, int32(10), got.GetRuleType())
+	assert.True(t, got.GetRoot())
+}
+
+func TestGetTargetGraphResponseToProto_Metadata(t *testing.T) {
+	t.Parallel()
+
+	chunk := entity.GetTargetGraphResponse{
+		Metadata: &entity.Metadata{
+			TargetIDMapping: map[int32]string{1: "//pkg:a", 2: "//pkg:b"},
+			RuleTypeMapping: map[int32]string{10: "go_library"},
+		},
+	}
+
+	proto := GetTargetGraphResponseToProto(&chunk)
+	meta := proto.GetItem().(*tangopb.GetTargetGraphResponse_Metadata)
+	assert.Equal(t, map[int32]string{1: "//pkg:a", 2: "//pkg:b"}, meta.Metadata.GetTargetIdMapping())
+	assert.Equal(t, map[int32]string{10: "go_library"}, meta.Metadata.GetRuleTypeMapping())
+}
diff --git a/mapper/BUILD.bazel b/mapper/BUILD.bazel
new file mode 100644
index 00000000..ea640a95
--- /dev/null
+++ b/mapper/BUILD.bazel
@@ -0,0 +1,25 @@
+load("@rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "mapper",
+    srcs = ["mapper.go"],
+    importpath = "github.com/uber/tango/mapper",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//core/targethasher",
+        "//entity",
+        "//internal/mapper/idmapper",
+        "@com_github_bazelbuild_buildtools//build_proto",
+    ],
+)
+
+go_test(
+    name = "mapper_test",
+    srcs = ["mapper_test.go"],
+    embed = [":mapper"],
+    deps = [
+        "//core/targethasher",
+        "@com_github_stretchr_testify//assert",
+        "@com_github_stretchr_testify//require",
+    ],
+)
diff --git a/mapper/mapper.go b/mapper/mapper.go
new file mode 100644
index 00000000..92fa0f54
--- /dev/null
+++ b/mapper/mapper.go
@@ -0,0 +1,97 @@
+package mapper
+
+import (
+	"context"
+	"encoding/hex"
+
+	buildpb "github.com/bazelbuild/buildtools/build_proto"
+	"github.com/uber/tango/core/targethasher"
+	"github.com/uber/tango/entity"
+	"github.com/uber/tango/internal/mapper/idmapper"
+)
+
+const cancelCheckInterval = 4096
+
+// ResultToTargetGraph converts a targethasher.Result into ID-mapped entity
+// types. Returns a flat list of targets and their accompanying metadata.
+// No chunking or proto conversion is performed.
+func ResultToTargetGraph(ctx context.Context, result targethasher.Result) ([]entity.OptimizedTarget, *entity.Metadata, error) {
+	targetNamesMapping := make(map[string]int32, len(result.TargetNames))
+	for i, name := range result.TargetNames {
+		targetNamesMapping[name] = int32(i + 1)
+	}
+
+	ruleTypeMapper := idmapper.NewMapper()
+	tagMapper := idmapper.NewMapper()
+	attrNameMapper := idmapper.NewMapper()
+	attrStrValMapper := idmapper.NewMapper()
+
+	targets := make([]entity.OptimizedTarget, 0, len(result.TargetNames))
+
+	n := 0
+	for _, name := range result.TargetNames {
+		t, ok := result.Targets[name]
+		if !ok {
+			continue
+		}
+		if n%cancelCheckInterval == 0 {
+			if err := ctx.Err(); err != nil {
+				return nil, nil, err
+			}
+		}
+		n++
+
+		depIDs := make([]int32, 0, len(t.Deps))
+		for _, depName := range t.Deps {
+			if depID, ok := targetNamesMapping[depName]; ok {
+				depIDs = append(depIDs, depID)
+			}
+		}
+
+		idt := entity.OptimizedTarget{
+			ID:                 targetNamesMapping[name],
+			Hash:               hex.EncodeToString(t.Hash),
+			DirectDependencies: depIDs,
+			Root:               t.Root,
+			External:           t.External,
+		}
+		if t.RuleType != "" {
+			idt.RuleType = ruleTypeMapper.ID(t.RuleType)
+		}
+		if len(t.Tags) > 0 {
+			tagIDs := make([]int32, 0, len(t.Tags))
+			for _, tag := range t.Tags {
+				tagIDs = append(tagIDs, tagMapper.ID(tag))
+			}
+			idt.Tags = tagIDs
+		}
+		if len(t.Attributes) > 0 {
+			attrs := make(map[int32]int32, len(t.Attributes))
+			for _, attr := range t.Attributes {
+				if attr.GetType() == buildpb.Attribute_STRING && attr.Name != nil && attr.StringValue != nil {
+					attrs[attrNameMapper.ID(*attr.Name)] = attrStrValMapper.ID(*attr.StringValue)
+				}
+			}
+			if len(attrs) > 0 {
+				idt.Attributes = attrs
+			}
+		}
+
+		targets = append(targets, idt)
+	}
+
+	targetIDToName := make(map[int32]string, len(targetNamesMapping))
+	for s, id := range targetNamesMapping {
+		targetIDToName[id] = s
+	}
+
+	meta := &entity.Metadata{
+		TargetIDMapping:             targetIDToName,
+		RuleTypeMapping:             ruleTypeMapper.Invert(),
+		TagMapping:                  tagMapper.Invert(),
+		AttributeNameMapping:        attrNameMapper.Invert(),
+		AttributeStringValueMapping: attrStrValMapper.Invert(),
+	}
+
+	return targets, meta, nil
+}
diff --git a/mapper/mapper_test.go b/mapper/mapper_test.go
new file mode 100644
index 00000000..3641f7ea
--- /dev/null
+++ b/mapper/mapper_test.go
@@ -0,0 +1,19 @@
+package mapper
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/uber/tango/core/targethasher"
+)
+
+func TestResultToTargetGraph_EmptyResult(t *testing.T) {
+	t.Parallel()
+
+	targets, meta, err := ResultToTargetGraph(t.Context(), targethasher.Result{})
+	require.NoError(t, err)
+	assert.Empty(t, targets)
+	assert.NotNil(t, meta)
+}