diff --git a/cmd/lk/simulate.go b/cmd/lk/simulate.go
index 4f131e70..f96f1760 100644
--- a/cmd/lk/simulate.go
+++ b/cmd/lk/simulate.go
@@ -389,10 +389,12 @@ func scenarioGroupToYAML(group *livekit.ScenarioGroup) ([]byte, error) {
 
 // scenariosFile mirrors a scenarios.yaml; `userdata` is a nested mapping here
 // and JSON-encoded into the proto's string field. Each `nodes` entry is a
-// SimulatorNode in protojson form.
+// SimulatorNode in protojson form. `include` names files whose nodes join this
+// file's (see simulate_include.go).
 type scenariosFile struct {
 	ID        string         `yaml:"id"`
 	Name      string         `yaml:"name"`
+	Include   []string       `yaml:"include,omitempty"`
 	Nodes     map[string]any `yaml:"nodes,omitempty"`
 	Scenarios []yamlScenario `yaml:"scenarios"`
 }
@@ -469,15 +471,19 @@ func loadScenarioGroup(path string) (*livekit.ScenarioGroup, error) {
 		return nil, fmt.Errorf("scenarios file has no id")
 	}
 	group := &livekit.ScenarioGroup{Id: f.ID, Name: f.Name}
-	names := make([]string, 0, len(f.Nodes))
-	for name := range f.Nodes {
+	nodes, err := resolveNodes(path, f.Nodes, f.Include)
+	if err != nil {
+		return nil, err
+	}
+	names := make([]string, 0, len(nodes))
+	for name := range nodes {
 		names = append(names, name)
 	}
 	sort.Strings(names)
 	for _, name := range names {
 		node := &livekit.SimulatorNode{}
-		if err := yamlValueToProto(f.Nodes[name], node); err != nil {
-			return nil, fmt.Errorf("node %q: %w", name, err)
+		if err := yamlValueToProto(nodes[name].value, node); err != nil {
+			return nil, fmt.Errorf("node %q (%s): %w", name, filepath.Base(nodes[name].file), err)
 		}
 		if group.Nodes == nil {
 			group.Nodes = map[string]*livekit.SimulatorNode{}
diff --git a/cmd/lk/simulate_include.go b/cmd/lk/simulate_include.go
new file mode 100644
index 00000000..9f6f6d68
--- /dev/null
+++ b/cmd/lk/simulate_include.go
@@ -0,0 +1,146 @@
+// Copyright 2026 LiveKit, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+// includedFile is a scenarios.yaml `include` target: it only contributes
+// nodes, so running one file never runs scenarios it did not list itself.
+type includedFile struct {
+	Include []string       `yaml:"include"`
+	Nodes   map[string]any `yaml:"nodes"`
+}
+
+// sourcedNode is a node in YAML form and the file that defines it.
+type sourcedNode struct {
+	value any
+	file  string
+}
+
+// nodeResolver merges the nodes of a scenarios file and everything it
+// includes. Paths resolve relative to the file that names them, and each file
+// loads once by its real path, so a file reached through two includes is not a
+// duplicate.
+type nodeResolver struct {
+	root   string // directory errors name files relative to
+	loaded map[string]bool
+	chain  []string // real paths from the root file to the one loading now
+	nodes  map[string]sourcedNode
+}
+
+func resolveNodes(path string, nodes map[string]any, include []string) (map[string]sourcedNode, error) {
+	real, err := filepath.EvalSymlinks(path)
+	if err != nil {
+		return nil, err
+	}
+	r := &nodeResolver{
+		root:   filepath.Dir(real),
+		loaded: map[string]bool{real: true},
+		chain:  []string{real},
+		nodes:  map[string]sourcedNode{},
+	}
+	if err := r.add(real, nodes); err != nil {
+		return nil, err
+	}
+	if err := r.includeAll(real, include); err != nil {
+		return nil, err
+	}
+	return r.nodes, nil
+}
+
+func (r *nodeResolver) includeAll(from string, include []string) error {
+	for _, rel := range include {
+		path := rel
+		if !filepath.IsAbs(path) {
+			path = filepath.Join(filepath.Dir(from), rel)
+		}
+		real, err := filepath.EvalSymlinks(path)
+		if err != nil {
+			return fmt.Errorf("%s: include %q: %w", r.name(from), rel, err)
+		}
+		if slices.Contains(r.chain, real) {
+			return fmt.Errorf("include cycle: %s", r.chainNames(append(r.chain, real)))
+		}
+		if r.loaded[real] {
+			continue
+		}
+		r.loaded[real] = true
+		if err := r.load(real); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (r *nodeResolver) load(real string) error {
+	data, err := os.ReadFile(real)
+	if err != nil {
+		return fmt.Errorf("%s: %w", r.name(real), err)
+	}
+	var keys map[string]any
+	if err := yaml.Unmarshal(data, &keys); err != nil {
+		return fmt.Errorf("%s: %w", r.name(real), err)
+	}
+	for key := range keys {
+		if key != "nodes" && key != "include" {
+			return fmt.Errorf("%s: an included file holds only `nodes` and `include`, not %q", r.name(real), key)
+		}
+	}
+	var f includedFile
+	if err := yaml.Unmarshal(data, &f); err != nil {
+		return fmt.Errorf("%s: %w", r.name(real), err)
+	}
+	if err := r.add(real, f.Nodes); err != nil {
+		return err
+	}
+	r.chain = append(r.chain, real)
+	defer func() { r.chain = r.chain[:len(r.chain)-1] }()
+	return r.includeAll(real, f.Include)
+}
+
+func (r *nodeResolver) add(file string, nodes map[string]any) error {
+	for name, value := range nodes {
+		if prev, ok := r.nodes[name]; ok {
+			return fmt.Errorf("node %q is defined in both %s and %s", name, r.name(prev.file), r.name(file))
+		}
+		r.nodes[name] = sourcedNode{value: value, file: file}
+	}
+	return nil
+}
+
+// name is how errors refer to a file: relative to the root file's directory,
+// with forward slashes as in `include`.
+func (r *nodeResolver) name(real string) string {
+	if rel, err := filepath.Rel(r.root, real); err == nil {
+		return filepath.ToSlash(rel)
+	}
+	return real
+}
+
+func (r *nodeResolver) chainNames(chain []string) string {
+	names := make([]string, len(chain))
+	for i, p := range chain {
+		names[i] = r.name(p)
+	}
+	return strings.Join(names, " -> ")
+}
diff --git a/cmd/lk/simulate_include_test.go b/cmd/lk/simulate_include_test.go
new file mode 100644
index 00000000..426c3b23
--- /dev/null
+++ b/cmd/lk/simulate_include_test.go
@@ -0,0 +1,146 @@
+// Copyright 2026 LiveKit, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"slices"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// writeFiles writes each name -> content under one temp dir and returns it.
+func writeFiles(t *testing.T, files map[string]string) string {
+	t.Helper()
+	dir := t.TempDir()
+	for name, content := range files {
+		path := filepath.Join(dir, name)
+		require.NoError(t, os.MkdirAll(filepath.Dir(path), 0o755))
+		require.NoError(t, os.WriteFile(path, []byte(content), 0o644))
+	}
+	return dir
+}
+
+const includingScenarios = `
+id: SCNG_dental
+include: [nodes/menus.yaml, nodes/people.yaml]
+nodes:
+  greeting: { say: "Hi, you've reached Sam.", then: livekit/voicemail }
+scenarios:
+  - id: SCN_a
+    label: menu-to-sam
+    start: menu
+    agent_expectations: Presses 1, then confirms with Sam.
+`
+
+func TestIncludedNodesJoinTheGroup(t *testing.T) {
+	dir := writeFiles(t, map[string]string{
+		"dental.yaml": includingScenarios,
+		// nested, with a path relative to the including file
+		"nodes/menus.yaml": `
+include: [common.yaml]
+nodes:
+  menu:
+    say: "For Sam, press 1."
+    routes: [{ match: "1", to: sam }]
+    timeout: { after: 8s, to: goodbye }
+`,
+		// includes common.yaml too, so dental.yaml reaches it twice
+		"nodes/people.yaml": `
+include: [common.yaml]
+nodes:
+  sam: { instructions: You are Sam. }
+`,
+		"nodes/common.yaml": `
+nodes:
+  goodbye: { say: Goodbye., then: livekit/hangup }
+`,
+	})
+
+	group, err := loadScenarioGroup(filepath.Join(dir, "dental.yaml"))
+	require.NoError(t, err)
+
+	names := make([]string, 0, len(group.Nodes))
+	for name := range group.Nodes {
+		names = append(names, name)
+	}
+	slices.Sort(names)
+	require.Equal(t, []string{"goodbye", "greeting", "menu", "sam"}, names)
+	require.Equal(t, "sam", group.Nodes["menu"].Routes[0].To)
+	require.Equal(t, "menu", group.Scenarios[0].Start)
+}
+
+func TestIncludeErrors(t *testing.T) {
+	cases := []struct {
+		name  string
+		files map[string]string
+		want  string
+	}{
+		{
+			name: "a cycle prints the include chain",
+			files: map[string]string{
+				"dental.yaml":       includingScenarios,
+				"nodes/menus.yaml":  "include: [common.yaml]\nnodes: { menu: { say: hi, then: livekit/hangup } }\n",
+				"nodes/common.yaml": "include: [menus.yaml]\n",
+				"nodes/people.yaml": "nodes: { sam: { instructions: x } }\n",
+			},
+			want: "include cycle: dental.yaml -> nodes/menus.yaml -> nodes/common.yaml -> nodes/menus.yaml",
+		},
+		{
+			name: "a node defined in two files names both",
+			files: map[string]string{
+				"dental.yaml":       includingScenarios,
+				"nodes/menus.yaml":  "nodes: { menu: { say: hi, then: livekit/hangup } }\n",
+				"nodes/people.yaml": "nodes: { menu: { say: hello, then: livekit/hangup } }\n",
+			},
+			want: `node "menu" is defined in both nodes/menus.yaml and nodes/people.yaml`,
+		},
+		{
+			name: "an included file cannot set scenarios",
+			files: map[string]string{
+				"dental.yaml":       includingScenarios,
+				"nodes/menus.yaml":  "nodes: { menu: { say: hi, then: livekit/hangup } }\nscenarios: []\n",
+				"nodes/people.yaml": "nodes: { sam: { instructions: x } }\n",
+			},
+			want: "nodes/menus.yaml: an included file holds only `nodes` and `include`, not \"scenarios\"",
+		},
+		{
+			name: "a missing include path",
+			files: map[string]string{
+				"dental.yaml":      includingScenarios,
+				"nodes/menus.yaml": "nodes: { menu: { say: hi, then: livekit/hangup } }\n",
+			},
+			want: `dental.yaml: include "nodes/people.yaml"`,
+		},
+		{
+			name: "a bad included node names its file",
+			files: map[string]string{
+				"dental.yaml":       includingScenarios,
+				"nodes/menus.yaml":  "nodes: { menu: { sya: hi } }\n",
+				"nodes/people.yaml": "nodes: { sam: { instructions: x } }\n",
+			},
+			want: `node "menu" (menus.yaml)`,
+		},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			dir := writeFiles(t, c.files)
+			_, err := loadScenarioGroup(filepath.Join(dir, "dental.yaml"))
+			require.ErrorContains(t, err, c.want)
+		})
+	}
+}