diff --git a/examples/lamp.js b/examples/lamp.js
index 5cc09ba..00ca34a 100644
--- a/examples/lamp.js
+++ b/examples/lamp.js
@@ -57,13 +57,25 @@ const partialTD = {
 };
 
 const thing = new Thing(partialTD);
+let currentOnValue = false;
+let currentLevelValue = 100;
 
 thing.setPropertyReadHandler('on', async function () {
-  return true;
+  return currentOnValue;
 });
 
 thing.setPropertyReadHandler('level', async function () {
-  return 50;
+  return currentLevelValue;
+});
+
+thing.setPropertyWriteHandler('on', async function (value) {
+  currentOnValue = value;
+  return;
+});
+
+thing.setPropertyWriteHandler('level', async function (value) {
+  currentLevelValue = value;
+  return;
 });
 
 const server = new ThingServer(thing);
diff --git a/src/property-affordance.js b/src/property-affordance.js
index 3bb86ff..e13f8c6 100644
--- a/src/property-affordance.js
+++ b/src/property-affordance.js
@@ -168,18 +168,27 @@ class PropertyAffordance extends InteractionAffordance {
   /**
    * Set read handler function.
    *
-   * @param {function} handler A function to handle property reads.
+   * @param {() => Promise<any>} handler An asynchronous function to handle property reads.
    */
   setReadHandler(handler) {
     this.readHandler = handler;
   }
 
+  /**
+   * Set write handler function.
+   *
+   * @param {(value: any) => Promise<void>} handler An asynchronous function to handle property writes.
+   */
+  setWriteHandler(handler) {
+    this.writeHandler = handler;
+  }
+
   /**
    * Read the property.
    *
-   * @returns {any} The current value of the property.
+   * @returns {Promise<any>} The current value of the property.
    */
-  read() {
+  async read() {
     if (this.readHandler) {
       return this.readHandler();
     } else {
@@ -188,6 +197,22 @@ class PropertyAffordance extends InteractionAffordance {
     }
   }
 
+  /**
+   * Write the property.
+   *
+   * @param {any} value The value to write.
+   * @returns {Promise<void>} A Promise.
+   */
+  async write(value) {
+    // TODO: Check value against type in TD
+    if (this.writeHandler) {
+      return this.writeHandler(value);
+    } else {
+      console.error(`No write handler set for property ${this.name}`);
+      throw new Error('InternalError');
+    }
+  }
+
   /**
    * @returns {PropertyDescription}
    */
diff --git a/src/thing-server.js b/src/thing-server.js
index f988e39..8ac0886 100644
--- a/src/thing-server.js
+++ b/src/thing-server.js
@@ -13,6 +13,8 @@ class ThingServer {
   constructor(thing) {
     this.thing = thing;
     this.app = express();
+    // Use JSON middleware and allow bare primite values as valid JSON
+    this.app.use(express.json({ strict: false }));
     this.server = null;
 
     this.app.get(
@@ -59,6 +61,39 @@ class ThingServer {
         response.status(200).json(value);
       },
     );
+
+    this.app.put(
+      '/properties/:name',
+      /**
+       * @param {Request} request
+       * @param {Response} response
+       */
+      async (request, response) => {
+        // Make sure name is a string since param can also be array
+        const name = Array.isArray(request.params.name)
+          ? request.params.name[0]
+          : request.params.name;
+        const value = request.body;
+        try {
+          await this.thing.writeProperty(name, value);
+        } catch (error) {
+          const errorMessage =
+            error instanceof Error ? error.message : 'InternalError';
+          switch (errorMessage) {
+            case 'NotFoundError':
+              response.status(404).send();
+              break;
+            case 'InternalError':
+              response.status(500).send();
+              break;
+            default:
+              response.status(500).send();
+          }
+          return;
+        }
+        response.status(204).send();
+      },
+    );
   }
 
   /**
diff --git a/src/thing.js b/src/thing.js
index a8a1fc5..cb39bb3 100644
--- a/src/thing.js
+++ b/src/thing.js
@@ -300,7 +300,7 @@ class Thing {
    * Set Property Read Handler.
    *
    * @param {string} name The name of the property to handle.
-   * @param {function} handler A function to handle property reads.
+   * @param {() => Promise<any>} handler A function to handle property reads.
    */
   setPropertyReadHandler(name, handler) {
     let property = this.properties.get(name);
@@ -310,6 +310,20 @@ class Thing {
     property.setReadHandler(handler);
   }
 
+  /**
+   * Set Property Write Handler.
+   *
+   * @param {string} name The name of the property to handle.
+   * @param {(value: any) => Promise<void>} handler A function to handle property writes.
+   */
+  setPropertyWriteHandler(name, handler) {
+    let property = this.properties.get(name);
+    if (!property) {
+      throw new Error(`No property called ${name} could be found`);
+    }
+    property.setWriteHandler(handler);
+  }
+
   /**
    * Read Property.
    *
@@ -325,6 +339,23 @@ class Thing {
     }
     return property.read();
   }
+
+  /**
+   * Write Property.
+   *
+   * @param {string} name The name of the property to write.
+   * @param {any} value The property value to write.
+   * @returns {any} The current value of the property, with a format conforming
+   *   to its data schema in the Thing Description.
+   */
+  writeProperty(name, value) {
+    let property = this.properties.get(name);
+    if (!property) {
+      console.error(`No property called ${name} could be found`);
+      throw new Error('NotFoundError');
+    }
+    return property.write(value);
+  }
 }
 
 export default Thing;
diff --git a/test/thing-server.test.js b/test/thing-server.test.js
index 973e13f..3c23530 100644
--- a/test/thing-server.test.js
+++ b/test/thing-server.test.js
@@ -17,10 +17,14 @@ describe('ThingServer', () => {
 
   let server;
   let baseUrl;
+  let currentValue = true;
 
   before(async () => {
     const thing = new Thing(partialTD);
-    thing.setPropertyReadHandler('on', async () => true);
+    thing.setPropertyReadHandler('on', async () => currentValue);
+    thing.setPropertyWriteHandler('on', async (value) => {
+      currentValue = value;
+    });
     server = new ThingServer(thing);
     // Listen on a random available port to avoid port conflicts
     await new Promise((resolve) => {
@@ -65,4 +69,33 @@ describe('ThingServer', () => {
       assert.strictEqual(response.status, 404);
     });
   });
+
+  describe('PUT /properties/:name', () => {
+    it('should update the property value when the property exists', async () => {
+      const response = await fetch(baseUrl + '/properties/on', {
+        method: 'PUT',
+        headers: {
+          'Content-Type': 'application/json',
+        },
+        body: JSON.stringify(false),
+      });
+
+      assert.strictEqual(response.status, 204);
+      assert.strictEqual(currentValue, false);
+    });
+  });
+
+  describe('PUT /properties/:invalidname', () => {
+    it('should return 404 when the property does not exist', async () => {
+      const response = await fetch(baseUrl + '/properties/foo', {
+        method: 'PUT',
+        headers: {
+          'Content-Type': 'application/json',
+        },
+        body: JSON.stringify(true),
+      });
+
+      assert.strictEqual(response.status, 404);
+    });
+  });
 });
diff --git a/test/thing.test.js b/test/thing.test.js
index 4544adc..72d79e0 100644
--- a/test/thing.test.js
+++ b/test/thing.test.js
@@ -50,24 +50,68 @@ describe('Thing', () => {
     });
   });
 
-  describe('readProperty', () => {
-    it('should return the value from the property read handler', () => {
+  describe('setPropertyReadHandler', () => {
+    it('should register a handler for an existing property', async () => {
       const thing = new Thing(partialTD);
-      thing.setPropertyReadHandler('on', () => true);
-      const value = thing.readProperty('on');
+      thing.setPropertyReadHandler('on', async () => true);
+      const value = await thing.readProperty('on');
       assert.strictEqual(value, true);
     });
 
-    it('should support async property read handlers', async () => {
+    it('should throw when the property does not exist', () => {
+      const thing = new Thing(partialTD);
+      assert.throws(
+        () => thing.setPropertyReadHandler('missing', async () => {}),
+        /No property called missing could be found/,
+      );
+    });
+  });
+
+  describe('readProperty', () => {
+    it('should return the value from the property read handler', async () => {
       const thing = new Thing(partialTD);
-      thing.setPropertyReadHandler('on', async () => false);
+      thing.setPropertyReadHandler('on', async () => true);
       const value = await thing.readProperty('on');
-      assert.strictEqual(value, false);
+      assert.strictEqual(value, true);
+    });
+
+    it('should reject when no handler is registered', async () => {
+      const thing = new Thing(partialTD);
+      await assert.rejects(() => thing.readProperty('on'), /InternalError/);
+    });
+  });
+
+  describe('setPropertyWriteHandler', () => {
+    it('should register a handler for an existing property', async () => {
+      const thing = new Thing(partialTD);
+      thing.setPropertyWriteHandler('on', async (value) => value);
+      const value = await thing.writeProperty('on', true);
+      assert.strictEqual(value, true);
+    });
+
+    it('should throw when the property does not exist', () => {
+      const thing = new Thing(partialTD);
+      assert.throws(
+        () => thing.setPropertyWriteHandler('missing', async () => {}),
+        /No property called missing could be found/,
+      );
+    });
+  });
+
+  describe('writeProperty', () => {
+    it('should return the value from the property write handler', async () => {
+      const thing = new Thing(partialTD);
+      thing.setPropertyWriteHandler('on', async (value) => value);
+      const value = await thing.writeProperty('on', true);
+      assert.strictEqual(value, true);
     });
 
-    it('should throw when no handler is registered', () => {
+    it('should reject when no handler is registered', async () => {
       const thing = new Thing(partialTD);
-      assert.throws(() => thing.readProperty('on'));
+      await assert.rejects(
+        () => thing.writeProperty('on', true),
+        /InternalError/,
+      );
     });
   });
 });