diff --git a/index.html b/index.html
index fb8bcb3..4a2f1e2 100644
--- a/index.html
+++ b/index.html
@@ -33,7 +33,7 @@ <h2>Send a Yo</h2>
         <input id="recipient" />
       </p>
       <p>
-        <input type="submit" id="send" value="Send" />
+        <input type="button" id="send" value="Send" />
       </p>
     </form>
   </main>
@@ -59,6 +59,18 @@ <h2>Send a Yo</h2>
       elements.from.innerText = await from;
       elements.to.innerText = await to;
     }
+
+    // Add a Yo on click
+    elements.send.addEventListener('click', async () => {
+      const from = 'https://ruben.verborgh.org/profile/#me';
+      const to = elements.recipient.value;
+      try {
+        await source.addYo({ from, to });
+      }
+      catch (error) {
+        alert(`Could not send Yo: ${error.message}`);
+      }
+    });
   </script>
 </body>
 </html>
diff --git a/scripts/YoSource.js b/scripts/YoSource.js
index 8bd1e39..693d11e 100644
--- a/scripts/YoSource.js
+++ b/scripts/YoSource.js
@@ -63,6 +63,25 @@ class YoSource {
     return yos[Math.floor(Math.random() * yos.length)];
   }
 
+  // Adds a Yo to the source
+  async addYo({ from, to }) {
+    // Create the SPARQL UPDATE query
+    const query = `
+      INSERT DATA {
+        [] <${AS}actor>   <${this._escape(from)}>;
+           <${AS}to>      <${this._escape(to)}>;
+           <${AS}summary> "Yo"@en.
+      }`
+    // Send a PATCH request to update the source
+    const response = await this._fetch(this._source, {
+      method: 'PATCH',
+      headers: { 'Content-Type': 'application/sparql-update' },
+      body: query,
+      credentials: 'include',
+    });
+    return response.status === 200;
+  }
+
   // Obtains a label for the given entity
   async _getLabel(entity) {
     // Try dereferencing the entity to obtain its label
@@ -84,4 +103,12 @@ class YoSource {
       return entity.value;
     }
   }
+
+  // Escapes the IRI for use in a SPARQL query
+  _escape (iri) {
+    // More of a sanity check, really
+    if (!iri || !/^\w+:[^<> ]+$/.test(iri))
+      throw new Error(`Invalid IRI: ${iri}`);
+    return iri;
+  }
 }