diff --git a/src/parser/PhutilURI.php b/src/parser/PhutilURI.php
--- a/src/parser/PhutilURI.php
+++ b/src/parser/PhutilURI.php
@@ -1,7 +1,16 @@
 <?php
 
 /**
- * Basic URI parser object.
+ * Structural representation of a URI.
+ *
+ * This class handles URIs of two types: standard URIs and Git URIs.
+ *
+ * Standard URIs look like `proto://user:pass@domain:port/path?query#fragment`.
+ * Almost all URIs are in this form.
+ *
+ * Git URIs look like `user@host:path`. These URIs are used by Git and SCP
+ * and have an implicit "ssh" protocol, no port, and interpret paths as
+ * relative instead of absolute.
  */
 final class PhutilURI extends Phobject {
 
@@ -13,10 +22,31 @@
   private $path;
   private $query = array();
   private $fragment;
+  private $type;
+
+  const TYPE_URI = 'uri';
+  const TYPE_GIT = 'git';
+
+  const INVALID_PATH = '<invalid-path>';
 
   public function __construct($uri) {
+    if ($uri instanceof PhutilURI) {
+      $this->protocol = $uri->protocol;
+      $this->user = $uri->user;
+      $this->pass = $uri->pass;
+      $this->domain = $uri->domain;
+      $this->port = $uri->port;
+      $this->path = $uri->path;
+      $this->query = $uri->query;
+      $this->fragment = $uri->fragment;
+      $this->type = $uri->type;
+      return;
+    }
+
     $uri = (string)$uri;
 
+    $type = self::TYPE_URI;
+
     $matches = null;
     if (preg_match('(^([^/:]*://[^/]*)(\\?.*)\z)', $uri, $matches)) {
       // If the URI is something like `idea://open?file=/path/to/file`, the
@@ -26,6 +56,25 @@
 
       $parts = parse_url($matches[1].'/'.$matches[2]);
       unset($parts['path']);
+    } else if (preg_match('(^[^/]+:(?!//))', $uri)) {
+      // Handle Git/SCP URIs in the form "user@domain:relative/path".
+
+      $user = '(?:(?P<user>[^/@]+)@)?';
+      $host = '(?P<host>[^/:]+)';
+      $path = ':(?P<path>.*)';
+
+      $ok = preg_match('(^\s*'.$user.$host.$path.'\z)', $uri, $matches);
+      if (!$ok) {
+        throw new Exception(
+          pht(
+            'Failed to parse URI "%s" as a Git URI.',
+            $uri));
+      }
+
+      $parts = $matches;
+      $parts['scheme'] = 'ssh';
+
+      $type = self::TYPE_GIT;
     } else {
       $parts = parse_url($uri);
     }
@@ -39,7 +88,6 @@
       }
     }
 
-
     // NOTE: `parse_url()` is very liberal about host names; fail the parse if
     // the host looks like garbage.
     if ($parts) {
@@ -56,35 +104,60 @@
     // stringyness is to preserve API compatibility and
     // allow the tests to continue passing
     $this->protocol = idx($parts, 'scheme', '');
-    $this->user     = rawurldecode(idx($parts, 'user', ''));
-    $this->pass     = rawurldecode(idx($parts, 'pass', ''));
-    $this->domain   = idx($parts, 'host', '');
-    $this->port     = (string)idx($parts, 'port', '');
-    $this->path     = idx($parts, 'path', '');
+    $this->user = rawurldecode(idx($parts, 'user', ''));
+    $this->pass = rawurldecode(idx($parts, 'pass', ''));
+    $this->domain = idx($parts, 'host', '');
+    $this->port = (string)idx($parts, 'port', '');
+    $this->path = idx($parts, 'path', '');
     $query = idx($parts, 'query');
     if ($query) {
       $this->query = id(new PhutilQueryStringParser())->parseQueryString(
         $query);
     }
     $this->fragment = idx($parts, 'fragment', '');
+
+    $this->type = $type;
   }
 
   public function __toString() {
     $prefix = null;
-    if ($this->protocol || $this->domain || $this->port) {
-      $protocol = nonempty($this->protocol, 'http');
-
-      $auth = '';
-      if (strlen($this->user) && strlen($this->pass)) {
-        $auth = rawurlencode($this->user).':'.
-                rawurlencode($this->pass).'@';
-      } else if (strlen($this->user)) {
-        $auth = rawurlencode($this->user).'@';
+
+    if ($this->isGitURI()) {
+      $port = null;
+    } else {
+      $port = $this->port;
+    }
+
+    $domain = $this->domain;
+
+    $user = $this->user;
+    $pass = $this->pass;
+    if (strlen($user) && strlen($pass)) {
+      $auth = rawurlencode($user).':'.rawurlencode($pass).'@';
+    } else if (strlen($user)) {
+      $auth = rawurlencode($user).'@';
+    } else {
+      $auth = null;
+    }
+
+    $protocol = $this->protocol;
+    if ($this->isGitURI()) {
+      $protocol = null;
+    } else {
+      if (strlen($auth)) {
+        $protocol = nonempty($this->protocol, 'http');
       }
+    }
 
-      $prefix = $protocol.'://'.$auth.$this->domain;
-      if ($this->port) {
-        $prefix .= ':'.$this->port;
+    if (strlen($protocol) || strlen($auth) || strlen($domain)) {
+      if ($this->isGitURI()) {
+        $prefix = "{$auth}{$domain}";
+      } else {
+        $prefix = "{$protocol}://{$auth}{$domain}";
+      }
+
+      if (strlen($port)) {
+        $prefix .= ':'.$port;
       }
     }
 
@@ -100,8 +173,14 @@
       $fragment = null;
     }
 
+    $path = $this->getPath();
+    if ($this->isGitURI()) {
+      if (strlen($path)) {
+        $path = ':'.$path;
+      }
+    }
 
-    return $prefix.$this->getPath().$query.$fragment;
+    return $prefix.$path.$query.$fragment;
   }
 
   public function setQueryParam($key, $value) {
@@ -126,6 +205,7 @@
     $this->protocol = $protocol;
     return $this;
   }
+
   public function getProtocol() {
     return $this->protocol;
   }
@@ -161,9 +241,14 @@
   }
 
   public function setPath($path) {
-    if ($this->domain && strlen($path) && $path[0] !== '/') {
-      $path = '/'.$path;
+    if ($this->isGitURI()) {
+      // Git URIs use relative paths which do not need to begin with "/".
+    } else {
+      if ($this->domain && strlen($path) && $path[0] !== '/') {
+        $path = '/'.$path;
+      }
     }
+
     $this->path = $path;
     return $this;
   }
@@ -221,4 +306,33 @@
     return $altered;
   }
 
+  public function isGitURI() {
+    return ($this->type == self::TYPE_GIT);
+  }
+
+  public function setType($type) {
+
+    if ($type == self::TYPE_URI) {
+      $path = $this->getPath();
+      if (strlen($path) && ($path[0] !== '/')) {
+        // Try to catch this here because we are not allowed to throw from
+        // inside __toString() so we don't have a reasonable opportunity to
+        // react properly if we catch it later.
+        throw new Exception(
+          pht(
+            'Unable to convert URI "%s" into a standard URI because the '.
+            'path is relative. Standard URIs can not represent relative '.
+            'paths.',
+            $this));
+      }
+    }
+
+    $this->type = $type;
+    return $this;
+  }
+
+  public function getType() {
+    return $this->type;
+  }
+
 }
diff --git a/src/parser/__tests__/PhutilURITestCase.php b/src/parser/__tests__/PhutilURITestCase.php
--- a/src/parser/__tests__/PhutilURITestCase.php
+++ b/src/parser/__tests__/PhutilURITestCase.php
@@ -95,6 +95,9 @@
     $this->assertEqual('good.com', $uri->getDomain());
     $this->assertEqual('http://good.com?u%3Ap%40evil.com%2F=', (string)$uri);
 
+    $uri = new PhutilURI('www.example.com');
+    $this->assertEqual('', $uri->getProtocol());
+    $this->assertEqual('www.example.com', (string)$uri);
   }
 
   public function testURIGeneration() {
@@ -164,4 +167,43 @@
     $this->assertEqual('', $uri->getPortWithProtocolDefault());
   }
 
+  public function testGitURIParsing() {
+    $uri = new PhutilURI('git@host.com:path/to/something');
+    $this->assertEqual('ssh', $uri->getProtocol());
+    $this->assertEqual('git', $uri->getUser());
+    $this->assertEqual('host.com', $uri->getDomain());
+    $this->assertEqual('path/to/something', $uri->getPath());
+    $this->assertEqual('git@host.com:path/to/something', (string)$uri);
+
+    $uri = new PhutilURI('host.com:path/to/something');
+    $this->assertEqual('ssh', $uri->getProtocol());
+    $this->assertEqual('', $uri->getUser());
+    $this->assertEqual('host.com', $uri->getDomain());
+    $this->assertEqual('path/to/something', $uri->getPath());
+    $this->assertEqual('host.com:path/to/something', (string)$uri);
+
+    $uri_1 = new PhutilURI('host.com:path/to/something');
+    $uri_2 = new PhutilURI($uri_1);
+
+    $this->assertEqual((string)$uri_1, (string)$uri_2);
+  }
+
+  public function testStrictGitURIParsingOfLeadingWhitespace() {
+    $uri = new PhutilURI(' user@example.com:path');
+    $this->assertEqual('', $uri->getDomain());
+  }
+
+  public function testNoRelativeURIPaths() {
+    $uri = new PhutilURI('user@example.com:relative_path');
+
+    $caught = null;
+    try {
+      $uri->setType(PhutilURI::TYPE_URI);
+    } catch (Exception $ex) {
+      $caught = $ex;
+    }
+
+    $this->assertTrue($caught instanceof Exception);
+  }
+
 }