diff --git a/src/parser/calendar/data/PhutilCalendarAbsoluteDateTime.php b/src/parser/calendar/data/PhutilCalendarAbsoluteDateTime.php
--- a/src/parser/calendar/data/PhutilCalendarAbsoluteDateTime.php
+++ b/src/parser/calendar/data/PhutilCalendarAbsoluteDateTime.php
@@ -51,11 +51,30 @@
         ->setHour((int)$matches['h'])
         ->setMinute((int)$matches['i'])
         ->setSecond((int)$matches['s']);
+    } else {
+      $datetime
+        ->setIsAllDay(true);
     }
 
     return $datetime;
   }
 
+  public static function newFromEpoch($epoch, $timezone = 'UTC') {
+    $date = new DateTime('@'.$epoch);
+
+    $zone = new DateTimeZone($timezone);
+    $date->setTimezone($zone);
+
+    return id(new self())
+      ->setYear((int)$date->format('Y'))
+      ->setMonth((int)$date->format('m'))
+      ->setDay((int)$date->format('d'))
+      ->setHour((int)$date->format('H'))
+      ->setMinute((int)$date->format('i'))
+      ->setSecond((int)$date->format('s'))
+      ->setTimezone($timezone);
+  }
+
   public function setYear($year) {
     $this->year = $year;
     return $this;
diff --git a/src/parser/calendar/data/PhutilCalendarDateTime.php b/src/parser/calendar/data/PhutilCalendarDateTime.php
--- a/src/parser/calendar/data/PhutilCalendarDateTime.php
+++ b/src/parser/calendar/data/PhutilCalendarDateTime.php
@@ -4,6 +4,7 @@
   extends Phobject {
 
   private $viewerTimezone;
+  private $isAllDay = false;
 
   public function setViewerTimezone($viewer_timezone) {
     $this->viewerTimezone = $viewer_timezone;
@@ -14,6 +15,15 @@
     return $this->viewerTimezone;
   }
 
+  public function setIsAllDay($is_all_day) {
+    $this->isAllDay = $is_all_day;
+    return $this;
+  }
+
+  public function getIsAllDay() {
+    return $this->isAllDay;
+  }
+
   public function getEpoch() {
     $datetime = $this->newPHPDateTime();
     return (int)$datetime->format('U');
@@ -22,7 +32,12 @@
   public function getISO8601() {
     $datetime = $this->newPHPDateTime();
     $datetime->setTimezone(new DateTimeZone('UTC'));
-    return $datetime->format('Ymd\\THis\\Z');
+
+    if ($this->getIsAllDay()) {
+      return $datetime->format('Ymd');
+    } else {
+      return $datetime->format('Ymd\\THis\\Z');
+    }
   }
 
   abstract protected function newPHPDateTimeZone();
diff --git a/src/parser/calendar/data/PhutilCalendarProxyDateTime.php b/src/parser/calendar/data/PhutilCalendarProxyDateTime.php
--- a/src/parser/calendar/data/PhutilCalendarProxyDateTime.php
+++ b/src/parser/calendar/data/PhutilCalendarProxyDateTime.php
@@ -23,6 +23,15 @@
     return $this->getProxy()->getViewerTimezone();
   }
 
+  public function setIsAllDay($is_all_day) {
+    $this->getProxy()->setIsAllDay($is_all_day);
+    return $this;
+  }
+
+  public function getIsAllDay() {
+    return $this->getProxy()->getIsAllDay();
+  }
+
   protected function newPHPDateTimezone() {
     return $this->getProxy()->newPHPDateTimezone();
   }
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
@@ -56,7 +56,7 @@
 
       foreach ($property['parameters'] as $parameter) {
         $paramname = $parameter['name'];
-        $paramvalue = 'TODO';
+        $paramvalue = $parameter['value'];
         $propline[] = ";{$paramname}={$paramvalue}";
       }
 
@@ -95,14 +95,14 @@
       // If adding this character would bring the line over 75 bytes, start
       // a new line.
       if (strlen($buf) + strlen($character) > 75) {
-        $out[] = $buf."\n";
+        $out[] = $buf."\r\n";
         $buf = ' ';
       }
 
       $buf .= $character;
     }
 
-    $out[] = $buf."\n";
+    $out[] = $buf."\r\n";
 
     return implode('', $out);
   }
@@ -110,7 +110,7 @@
   private function getNodeProperties(PhutilCalendarNode $node) {
     switch ($node->getNodeType()) {
       case PhutilCalendarDocumentNode::NODETYPE:
-        return array();
+        return $this->getDocumentNodeProperties($node);
       case PhutilCalendarEventNode::NODETYPE:
         return $this->getEventNodeProperties($node);
       default:
@@ -118,6 +118,21 @@
     }
   }
 
+  private function getDocumentNodeProperties(
+    PhutilCalendarDocumentNode $event) {
+    $properties = array();
+
+    $properties[] = $this->newTextProperty(
+      'VERSION',
+      '2.0');
+
+    $properties[] = $this->newTextProperty(
+      'PRODID',
+      '-//Phacility//Phabricator//EN');
+
+    return $properties;
+  }
+
   private function getEventNodeProperties(PhutilCalendarEventNode $event) {
     $properties = array();
 
@@ -208,6 +223,16 @@
     PhutilCalendarDateTime $value,
     array $parameters = array()) {
     $datetime = $value->getISO8601();
+
+    if ($value->getIsAllDay()) {
+      $parameters[] = array(
+        'name' => 'VALUE',
+        'values' => array(
+          'DATE',
+        ),
+      );
+    }
+
     return $this->newProperty($name, $datetime, $parameters);
   }
 
@@ -216,12 +241,39 @@
     $value,
     array $parameters = array()) {
 
-    // TODO: Actually handle parameters.
+    $map = array(
+      '^' => '^^',
+      "\n" => '^n',
+      '"' => "^'",
+    );
+
+    $writable_params = array();
+    foreach ($parameters as $k => $parameter) {
+      $value_list = array();
+      foreach ($parameter['values'] as $v) {
+        $v = str_replace(array_keys($map), array_values($map), $v);
+
+        // If the parameter value isn't a very simple one, quote it.
+
+        // 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)) {
+          $v = '"'.$v.'"';
+        }
+
+        $value_list[] = $v;
+      }
+
+      $writable_params[] = array(
+        'name' => $parameter['name'],
+        'value' => implode(',', $value_list),
+      );
+    }
 
     return array(
       'name' => $name,
       'value' => $value,
-      'parameters' => array(),
+      'parameters' => $writable_params,
     );
   }
 
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
@@ -2,7 +2,7 @@
 
 final class PhutilICSWriterTestCase extends PhutilTestCase {
 
-  public function testICSWriter() {
+  public function testICSWriterTeaTime() {
     $teas = array(
       'earl grey tea',
       'English breakfast tea',
@@ -37,6 +37,25 @@
     $this->assertICS('writer-tea-time.ics', $ics_data);
   }
 
+  public function testICSWriterAllDay() {
+    $event = id(new PhutilCalendarEventNode())
+      ->setUID('christmas-day')
+      ->setName('Christmas 2016')
+      ->setDescription('A minor religious holiday.')
+      ->setCreatedDateTime(
+        PhutilCalendarAbsoluteDateTime::newFromISO8601('20160901T232425Z'))
+      ->setModifiedDateTime(
+        PhutilCalendarAbsoluteDateTime::newFromISO8601('20160901T232425Z'))
+      ->setStartDateTime(
+        PhutilCalendarAbsoluteDateTime::newFromISO8601('20161225'))
+      ->setEndDateTime(
+        PhutilCalendarAbsoluteDateTime::newFromISO8601('20161226'));
+
+    $ics_data = $this->writeICSSingleEvent($event);
+
+    $this->assertICS('writer-christmas.ics', $ics_data);
+  }
+
   private function writeICSSingleEvent(PhutilCalendarEventNode $event) {
     $calendar = id(new PhutilCalendarDocumentNode())
       ->appendChild($event);
diff --git a/src/parser/calendar/ics/__tests__/data/writer-christmas.ics b/src/parser/calendar/ics/__tests__/data/writer-christmas.ics
new file mode 100644
--- /dev/null
+++ b/src/parser/calendar/ics/__tests__/data/writer-christmas.ics
@@ -0,0 +1,13 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Phacility//Phabricator//EN
+BEGIN:VEVENT
+UID:christmas-day
+CREATED:20160901T232425Z
+DTSTAMP:20160901T232425Z
+DTSTART;VALUE=DATE:20161225
+DTEND;VALUE=DATE:20161226
+SUMMARY:Christmas 2016
+DESCRIPTION:A minor religious holiday.
+END:VEVENT
+END:VCALENDAR
diff --git a/src/parser/calendar/ics/__tests__/data/writer-tea-time.ics b/src/parser/calendar/ics/__tests__/data/writer-tea-time.ics
--- a/src/parser/calendar/ics/__tests__/data/writer-tea-time.ics
+++ b/src/parser/calendar/ics/__tests__/data/writer-tea-time.ics
@@ -1,14 +1,16 @@
-BEGIN:VCALENDAR
-BEGIN:VEVENT
-UID:tea-time
-CREATED:20160915T070000Z
-DTSTAMP:20160915T070000Z
-DTSTART:20160916T150000Z
-DTEND:20160916T160000Z
-SUMMARY:Tea Time
-DESCRIPTION:Tea and\, perhaps\, crumpets.\nYour presence is requested!\nThi
- s is a long list of types of tea to test line wrapping: earl grey tea\, En
- glish breakfast tea\, black tea\, green tea\, t-rex\, oolong tea\, mint te
- a\, tea with milk.
-END:VEVENT
-END:VCALENDAR
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Phacility//Phabricator//EN
+BEGIN:VEVENT
+UID:tea-time
+CREATED:20160915T070000Z
+DTSTAMP:20160915T070000Z
+DTSTART:20160916T150000Z
+DTEND:20160916T160000Z
+SUMMARY:Tea Time
+DESCRIPTION:Tea and\, perhaps\, crumpets.\nYour presence is requested!\nThi
+ s is a long list of types of tea to test line wrapping: earl grey tea\, En
+ glish breakfast tea\, black tea\, green tea\, t-rex\, oolong tea\, mint te
+ a\, tea with milk.
+END:VEVENT
+END:VCALENDAR