diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -143,6 +143,7 @@
     'PhutilCalendarRawNode' => 'parser/calendar/data/PhutilCalendarRawNode.php',
     'PhutilCalendarRelativeDateTime' => 'parser/calendar/data/PhutilCalendarRelativeDateTime.php',
     'PhutilCalendarRootNode' => 'parser/calendar/data/PhutilCalendarRootNode.php',
+    'PhutilCalendarUserNode' => 'parser/calendar/data/PhutilCalendarUserNode.php',
     'PhutilCallbackFilterIterator' => 'utils/PhutilCallbackFilterIterator.php',
     'PhutilCallbackSignalHandler' => 'future/exec/PhutilCallbackSignalHandler.php',
     'PhutilChannel' => 'channel/PhutilChannel.php',
@@ -726,6 +727,7 @@
     'PhutilCalendarRawNode' => 'PhutilCalendarContainerNode',
     'PhutilCalendarRelativeDateTime' => 'PhutilCalendarProxyDateTime',
     'PhutilCalendarRootNode' => 'PhutilCalendarContainerNode',
+    'PhutilCalendarUserNode' => 'PhutilCalendarNode',
     'PhutilCallbackFilterIterator' => 'FilterIterator',
     'PhutilCallbackSignalHandler' => 'PhutilSignalHandler',
     'PhutilChannel' => 'Phobject',
diff --git a/src/parser/calendar/data/PhutilCalendarEventNode.php b/src/parser/calendar/data/PhutilCalendarEventNode.php
--- a/src/parser/calendar/data/PhutilCalendarEventNode.php
+++ b/src/parser/calendar/data/PhutilCalendarEventNode.php
@@ -13,6 +13,8 @@
   private $duration;
   private $createdDateTime;
   private $modifiedDateTime;
+  private $organizer;
+  private $attendees = array();
 
   public function setUID($uid) {
     $this->uid = $uid;
@@ -99,4 +101,28 @@
     return $this->modifiedDateTime;
   }
 
+  public function setOrganizer(PhutilCalendarUserNode $organizer) {
+    $this->organizer = $organizer;
+    return $this;
+  }
+
+  public function getOrganizer() {
+    return $this->organizer;
+  }
+
+  public function setAttendees(array $attendees) {
+    assert_instances_of($attendees, 'PhutilCalendarUserNode');
+    $this->attendees = $attendees;
+    return $this;
+  }
+
+  public function getAttendees() {
+    return $this->attendees;
+  }
+
+  public function addAttendee(PhutilCalendarUserNode $attendee) {
+    $this->attendees[] = $attendee;
+    return $this;
+  }
+
 }
diff --git a/src/parser/calendar/data/PhutilCalendarUserNode.php b/src/parser/calendar/data/PhutilCalendarUserNode.php
new file mode 100644
--- /dev/null
+++ b/src/parser/calendar/data/PhutilCalendarUserNode.php
@@ -0,0 +1,40 @@
+<?php
+
+final class PhutilCalendarUserNode extends PhutilCalendarNode {
+
+  private $name;
+  private $uri;
+  private $status;
+
+  const STATUS_INVITED = 'invited';
+  const STATUS_ACCEPTED = 'accepted';
+  const STATUS_DECLINED = 'declined';
+
+  public function setName($name) {
+    $this->name = $name;
+    return $this;
+  }
+
+  public function getName() {
+    return $this->name;
+  }
+
+  public function setURI($uri) {
+    $this->uri = $uri;
+    return $this;
+  }
+
+  public function getURI() {
+    return $this->uri;
+  }
+
+  public function setStatus($status) {
+    $this->status = $status;
+    return $this;
+  }
+
+  public function getStatus() {
+    return $this->status;
+  }
+
+}
diff --git a/src/parser/calendar/ics/PhutilICSWriter.php b/src/parser/calendar/ics/PhutilICSWriter.php
--- a/src/parser/calendar/ics/PhutilICSWriter.php
+++ b/src/parser/calendar/ics/PhutilICSWriter.php
@@ -193,6 +193,22 @@
         $description);
     }
 
+    $organizer = $event->getOrganizer();
+    if ($organizer) {
+      $properties[] = $this->newUserProperty(
+        'ORGANIZER',
+        $organizer);
+    }
+
+    $attendees = $event->getAttendees();
+    if ($attendees) {
+      foreach ($attendees as $attendee) {
+        $properties[] = $this->newUserProperty(
+          'ATTENDEE',
+          $attendee);
+      }
+    }
+
     return $properties;
   }
 
@@ -236,6 +252,46 @@
     return $this->newProperty($name, $datetime, $parameters);
   }
 
+  private function newUserProperty(
+    $name,
+    PhutilCalendarUserNode $value,
+    array $parameters = array()) {
+
+    $parameters[] = array(
+      'name' => 'CN',
+      'values' => array(
+        $value->getName(),
+      ),
+    );
+
+    $partstat = null;
+    switch ($value->getStatus()) {
+      case PhutilCalendarUserNode::STATUS_INVITED:
+        $partstat = 'NEEDS-ACTION';
+        break;
+      case PhutilCalendarUserNode::STATUS_ACCEPTED:
+        $partstat = 'ACCEPTED';
+        break;
+      case PhutilCalendarUserNode::STATUS_DECLINED:
+        $partstat = 'DECLINED';
+        break;
+    }
+
+    if ($partstat !== null) {
+      $parameters[] = array(
+        'name' => 'PARTSTAT',
+        'values' => array(
+          $partstat,
+        ),
+      );
+    }
+
+    // TODO: We could reasonably fill in "ROLE" and "RSVP" here too, but it
+    // isn't clear if these are important to external programs or not.
+
+    return $this->newProperty($name, $value->getURI(), $parameters);
+  }
+
   private function newProperty(
     $name,
     $value,
@@ -257,7 +313,7 @@
 
         // RFC5545 says that we MUST quote it if it has a colon, a semicolon,
         // or a comma, and that we MUST quote it if it's a URI.
-        if (!preg_match('/^[A-Za-z0-9]*\z/', $v)) {
+        if (!preg_match('/^[A-Za-z0-9-]*\z/', $v)) {
           $v = '"'.$v.'"';
         }
 
diff --git a/src/parser/calendar/ics/__tests__/PhutilICSWriterTestCase.php b/src/parser/calendar/ics/__tests__/PhutilICSWriterTestCase.php
--- a/src/parser/calendar/ics/__tests__/PhutilICSWriterTestCase.php
+++ b/src/parser/calendar/ics/__tests__/PhutilICSWriterTestCase.php
@@ -56,6 +56,37 @@
     $this->assertICS('writer-christmas.ics', $ics_data);
   }
 
+  public function testICSWriterUsers() {
+    $event = id(new PhutilCalendarEventNode())
+      ->setUID('office-party')
+      ->setName('Office Party')
+      ->setCreatedDateTime(
+        PhutilCalendarAbsoluteDateTime::newFromISO8601('20161001T120000Z'))
+      ->setModifiedDateTime(
+        PhutilCalendarAbsoluteDateTime::newFromISO8601('20161001T120000Z'))
+      ->setStartDateTime(
+        PhutilCalendarAbsoluteDateTime::newFromISO8601('20161215T200000Z'))
+      ->setEndDateTime(
+        PhutilCalendarAbsoluteDateTime::newFromISO8601('20161215T230000Z'))
+      ->setOrganizer(
+        id(new PhutilCalendarUserNode())
+          ->setName('Big Boss')
+          ->setURI('mailto:big.boss@example.com'))
+      ->addAttendee(
+        id(new PhutilCalendarUserNode())
+          ->setName('Milton')
+          ->setStatus(PhutilCalendarUserNode::STATUS_INVITED)
+          ->setURI('mailto:milton@example.com'))
+      ->addAttendee(
+        id(new PhutilCalendarUserNode())
+          ->setName('Nancy')
+          ->setStatus(PhutilCalendarUserNode::STATUS_ACCEPTED)
+          ->setURI('mailto:nancy@example.com'));
+
+    $ics_data = $this->writeICSSingleEvent($event);
+    $this->assertICS('writer-office-party.ics', $ics_data);
+  }
+
   private function writeICSSingleEvent(PhutilCalendarEventNode $event) {
     $calendar = id(new PhutilCalendarDocumentNode())
       ->appendChild($event);
diff --git a/src/parser/calendar/ics/__tests__/data/writer-office-party.ics b/src/parser/calendar/ics/__tests__/data/writer-office-party.ics
new file mode 100644
--- /dev/null
+++ b/src/parser/calendar/ics/__tests__/data/writer-office-party.ics
@@ -0,0 +1,15 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Phacility//Phabricator//EN
+BEGIN:VEVENT
+UID:office-party
+CREATED:20161001T120000Z
+DTSTAMP:20161001T120000Z
+DTSTART:20161215T200000Z
+DTEND:20161215T230000Z
+SUMMARY:Office Party
+ORGANIZER;CN="Big Boss":mailto:big.boss@example.com
+ATTENDEE;CN=Milton;PARTSTAT=NEEDS-ACTION:mailto:milton@example.com
+ATTENDEE;CN=Nancy;PARTSTAT=ACCEPTED:mailto:nancy@example.com
+END:VEVENT
+END:VCALENDAR