diff --git a/package.json b/package.json
index e24ab1e..df8cf41 100644
--- a/package.json
+++ b/package.json
@@ -35,6 +35,10 @@
     "./vcdm": {
       "types": "./dist/VCDM.d.ts",
       "default": "./dist/VCDM.js"
+    },
+    "./zcap": {
+      "types": "./dist/ZCap.d.ts",
+      "default": "./dist/ZCap.js"
     }
   },
   "devDependencies": {
diff --git a/src/ZCap.ts b/src/ZCap.ts
new file mode 100644
index 0000000..5669d86
--- /dev/null
+++ b/src/ZCap.ts
@@ -0,0 +1,98 @@
+/*!
+ * Authorization Capabilities (zCap) interfaces.
+ * @see https://w3c-ccg.github.io/zcap-spec/
+ */
+
+/**
+ * A proof attached to a delegated zCap.
+ */
+export interface ICapabilityDelegationProof {
+  /** The cryptographic suite type (e.g. `'Ed25519Signature2020'`). */
+  type: string
+  /** ISO 8601 date-time the proof was created. */
+  created: string
+  /** Verification method URI used to sign. */
+  verificationMethod: string
+  /** Always `'capabilityDelegation'`. */
+  proofPurpose: 'capabilityDelegation'
+  /**
+   * Ordered capability chain (root → parent). All entries are string IDs
+   * except the last delegated zCap, which is embedded as an object.
+   */
+  capabilityChain: Array<string | IDelegatedZcap>
+  /** The encoded proof value. */
+  proofValue: string
+}
+
+/**
+ * A root authorization capability (zCap). Root zCaps are unsigned, have no
+ * `expires` field and no delegation proof. Their `id` follows the convention
+ * `urn:zcap:root:${encodeURIComponent(invocationTarget)}`.
+ */
+export interface IRootZcap {
+  /** The zCap JSON-LD context URL. */
+  '@context': string
+  /** Capability ID (`urn:zcap:root:<encodedTarget>`). */
+  id: string
+  /** The DID(s) authorized to invoke. */
+  controller: string | string[]
+  /** Resource URI this capability grants access to (absolute URI). */
+  invocationTarget: string
+}
+
+/**
+ * A delegated authorization capability (zCap). Delegated capabilities narrow
+ * a parent capability and must carry exactly one `capabilityDelegation` proof.
+ */
+export interface IDelegatedZcap {
+  /** JSON-LD context array; first entry MUST be the zCap context URL. */
+  '@context': string[]
+  /** Capability ID (absolute URI). */
+  id: string
+  /** Parent capability ID (absolute URI). */
+  parentCapability: string
+  /** The DID(s) authorized to invoke. */
+  controller: string | string[]
+  /** Resource URI this capability grants access to (absolute URI). */
+  invocationTarget: string
+  /**
+   * The action(s) the controller may perform; if absent, no actions are
+   * allowed (except for the root zCap).
+   */
+  allowedAction?: string | string[]
+  /** ISO 8601 date-time when this capability expires. */
+  expires: string
+  /** The capability delegation proof(s). */
+  proof: ICapabilityDelegationProof | ICapabilityDelegationProof[]
+}
+
+/**
+ * A zCap is either a root or a delegated authorization capability.
+ *
+ * Use this discriminated union when the call site knows it has a real,
+ * well-formed zCap and can narrow via `'parentCapability' in cap`.
+ */
+export type IZcap = IRootZcap | IDelegatedZcap
+
+/**
+ * A permissive zCap shape that conflates root and delegated kinds and admits
+ * arbitrary additional properties (e.g. the opaque object returned from
+ * `jsigs.sign()`).
+ *
+ * Prefer the strict `IZcap` union when possible. Use `IZcapLike` only when:
+ * - the call site receives a capability whose kind is not yet known and
+ *   cannot reasonably discriminate, or
+ * - the call site needs to accept the open-ended shape produced by
+ *   linked-data signature libraries that may attach extra properties.
+ */
+export interface IZcapLike {
+  '@context': string | string[]
+  id: string
+  invocationTarget: string
+  controller?: string | string[]
+  parentCapability?: string
+  allowedAction?: string | string[]
+  expires?: string
+  proof?: ICapabilityDelegationProof | ICapabilityDelegationProof[]
+  [key: string]: unknown
+}
diff --git a/src/index.ts b/src/index.ts
index e0d77f6..5e9a955 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -6,3 +6,4 @@ export * from './DID.js'
 export * from './KeyPair.js'
 export * from './VCDM.js'
 export * from './OBv3.js'
+export * from './ZCap.js'
diff --git a/test/ZCap.spec.ts b/test/ZCap.spec.ts
new file mode 100644
index 0000000..55c8747
--- /dev/null
+++ b/test/ZCap.spec.ts
@@ -0,0 +1,74 @@
+import { describe, test } from 'node:test'
+import assert from 'node:assert'
+import {
+  ICapabilityDelegationProof,
+  IDelegatedZcap,
+  IRootZcap,
+  IZcap,
+  IZcapLike
+} from '../src'
+
+await describe('RootZcap', async () => {
+  await test('exists', async () => {
+    const root: IRootZcap = {
+      '@context': 'https://w3id.org/zcap/v1',
+      id: 'urn:zcap:root:https%3A%2F%2Fexample.com%2Fresource',
+      controller: 'did:example:alice',
+      invocationTarget: 'https://example.com/resource'
+    }
+
+    assert.ok(root)
+  })
+})
+
+await describe('DelegatedZcap', async () => {
+  await test('exists', async () => {
+    const proof: ICapabilityDelegationProof = {
+      type: 'Ed25519Signature2020',
+      created: '2026-01-01T00:00:00Z',
+      verificationMethod: 'did:example:alice#key-1',
+      proofPurpose: 'capabilityDelegation',
+      capabilityChain: [
+        'urn:zcap:root:https%3A%2F%2Fexample.com%2Fresource'
+      ],
+      proofValue: 'z3...'
+    }
+
+    const delegated: IDelegatedZcap = {
+      '@context': ['https://w3id.org/zcap/v1'],
+      id: 'urn:uuid:00000000-0000-0000-0000-000000000001',
+      parentCapability: 'urn:zcap:root:https%3A%2F%2Fexample.com%2Fresource',
+      controller: 'did:example:bob',
+      invocationTarget: 'https://example.com/resource',
+      allowedAction: ['GET'],
+      expires: '2026-12-31T23:59:59Z',
+      proof
+    }
+
+    assert.ok(delegated)
+  })
+})
+
+await describe('IZcap union', async () => {
+  await test('accepts root and delegated', async () => {
+    const root: IZcap = {
+      '@context': 'https://w3id.org/zcap/v1',
+      id: 'urn:zcap:root:https%3A%2F%2Fexample.com%2Fr',
+      controller: 'did:example:alice',
+      invocationTarget: 'https://example.com/r'
+    }
+    assert.ok(!('parentCapability' in root))
+  })
+})
+
+await describe('IZcapLike', async () => {
+  await test('admits extra properties', async () => {
+    const loose: IZcapLike = {
+      '@context': 'https://w3id.org/zcap/v1',
+      id: 'urn:zcap:root:https%3A%2F%2Fexample.com%2Fr',
+      invocationTarget: 'https://example.com/r',
+      arbitraryExtra: 'allowed'
+    }
+    assert.ok(loose)
+  })
+})