diff --git a/src/filesystem/FileFinder.php b/src/filesystem/FileFinder.php
--- a/src/filesystem/FileFinder.php
+++ b/src/filesystem/FileFinder.php
@@ -35,7 +35,9 @@
    * @task create
    */
   public function __construct($root) {
-    $this->root = rtrim($root, '/');
+    $this->root = rtrim(
+        $root,
+        phutil_is_windows() ? getenv('HOMEDRIVE') : '/');
   }
 
   /**
diff --git a/src/filesystem/Filesystem.php b/src/filesystem/Filesystem.php
--- a/src/filesystem/Filesystem.php
+++ b/src/filesystem/Filesystem.php
@@ -610,6 +610,17 @@
 
 /* -(  Directories  )-------------------------------------------------------- */
 
+  /**
+   * Build a path from the pieces provided using the system's directory
+   * separator.
+   *
+   * @param  ...string The list of directory paths to be joined
+   * @return string The built, full directory path.
+   */
+  public static function buildPath() {
+    return implode(DIRECTORY_SEPARATOR, func_get_args());
+  }
+
 
   /**
    * Create a directory in a manner similar to mkdir(), but throw detailed
@@ -766,6 +777,24 @@
    * @task   directory
    */
   public static function walkToRoot($path, $root = '/') {
+    if (phutil_is_windows()) {
+        $win_root = getenv('HOMEDRIVE');
+
+        $root = explode('/', $root);
+        $path = explode('/', $path);
+
+        if (!$root[0]) {
+          $root[0] = $win_root;
+        }
+
+        if (!$path[0]) {
+          $path[0] = $win_root;
+        }
+
+        $root = implode(DIRECTORY_SEPARATOR, $root);
+        $path = implode(DIRECTORY_SEPARATOR, $path);
+    }
+
     $path = self::resolvePath($path);
     $root = self::resolvePath($root);
 
@@ -798,7 +827,10 @@
         $next = DIRECTORY_SEPARATOR.implode(DIRECTORY_SEPARATOR, $parts);
       }
 
-      $walk[] = $next;
+      if ($next) {
+        $walk[] = $next;
+      }
+
       if ($next == $root) {
         break;
       }
diff --git a/src/filesystem/__tests__/FileFinderTestCase.php b/src/filesystem/__tests__/FileFinderTestCase.php
--- a/src/filesystem/__tests__/FileFinderTestCase.php
+++ b/src/filesystem/__tests__/FileFinderTestCase.php
@@ -9,8 +9,12 @@
     return $finder;
   }
 
+  protected function getModes() {
+    return phutil_is_windows()? array('php') : array('php', 'shell');
+  }
+
   public function testFinderWithChecksums() {
-    foreach (array('php', 'shell') as $mode) {
+    foreach ($this->getModes() as $mode) {
       $files = $this->getFinder()
         ->setGenerateChecksums(true)
         ->withType('f')
@@ -52,7 +56,7 @@
   }
 
   public function testFinderWithoutChecksums() {
-    foreach (array('php', 'shell') as $mode) {
+    foreach ($this->getModes() as $mode) {
       $files = $this->getFinder()
         ->withType('f')
         ->withPath('*')
@@ -77,7 +81,7 @@
   }
 
   public function testFinderWithDirectories() {
-    foreach (array('php', 'shell') as $mode) {
+    foreach ($this->getModes() as $mode) {
       $files = $this->getFinder()
         ->setGenerateChecksums(true)
         ->withPath('*')
@@ -105,7 +109,7 @@
   }
 
   public function testFinderWithPath() {
-    foreach (array('php', 'shell') as $mode) {
+    foreach ($this->getModes() as $mode) {
       $files = $this->getFinder()
         ->setGenerateChecksums(true)
         ->withType('f')
@@ -125,7 +129,7 @@
   }
 
   public function testFinderWithNames() {
-    foreach (array('php', 'shell') as $mode) {
+    foreach ($this->getModes() as $mode) {
       $files = $this->getFinder()
         ->withType('f')
         ->withPath('*')
diff --git a/src/filesystem/__tests__/FilesystemTestCase.php b/src/filesystem/__tests__/FilesystemTestCase.php
--- a/src/filesystem/__tests__/FilesystemTestCase.php
+++ b/src/filesystem/__tests__/FilesystemTestCase.php
@@ -74,25 +74,36 @@
   }
 
   public function testWalkToRoot() {
+    $win_root = phutil_is_windows() ? getenv('HOMEDRIVE') : '';
     $test_cases = array(
       array(
-        dirname(__FILE__).'/data/include_dir.txt/subdir.txt/test',
+        Filesystem::buildPath(
+          dirname(__FILE__),
+          'data', 'include_dir.txt', 'subdir.txt', 'test'),
         dirname(__FILE__),
         array(
-          dirname(__FILE__).'/data/include_dir.txt/subdir.txt/test',
-          dirname(__FILE__).'/data/include_dir.txt/subdir.txt',
-          dirname(__FILE__).'/data/include_dir.txt',
-          dirname(__FILE__).'/data',
+          Filesystem::buildPath(
+            dirname(__FILE__),
+            'data', 'include_dir.txt', 'subdir.txt', 'test'),
+          Filesystem::buildPath(
+            dirname(__FILE__),
+            'data', 'include_dir.txt', 'subdir.txt'),
+          Filesystem::buildPath(dirname(__FILE__), 'data', 'include_dir.txt'),
+          Filesystem::buildPath(dirname(__FILE__), 'data'),
           dirname(__FILE__),
         ),
       ),
       array(
-        dirname(__FILE__).'/data/include_dir.txt/subdir.txt',
+        Filesystem::buildPath(
+          dirname(__FILE__),
+          'data', 'include_dir.txt', 'subdir.txt'),
         dirname(__FILE__),
         array(
-          dirname(__FILE__).'/data/include_dir.txt/subdir.txt',
-          dirname(__FILE__).'/data/include_dir.txt',
-          dirname(__FILE__).'/data',
+          Filesystem::buildPath(
+            dirname(__FILE__),
+            'data', 'include_dir.txt', 'subdir.txt'),
+          Filesystem::buildPath(dirname(__FILE__), 'data', 'include_dir.txt'),
+          Filesystem::buildPath(dirname(__FILE__), 'data'),
           dirname(__FILE__),
         ),
       ),
@@ -107,19 +118,28 @@
 
       'root is not an ancestor of path' => array(
         dirname(__FILE__),
-        dirname(__FILE__).'/data/include_dir.txt/subdir.txt',
+        Filesystem::buildPath(
+          dirname(__FILE__), 'data', 'include_dir.txt', 'subdir.txt'),
         array(),
       ),
 
       'fictional paths work' => array(
         '/x/y/z',
         '/',
-        array(
-          '/x/y/z',
-          '/x/y',
-          '/x',
-          '/',
-        ),
+        phutil_is_windows() ?
+          array(
+            $win_root.'\\x\\y\\z',
+            $win_root.'\\x\\y',
+            $win_root.'\\x',
+            $win_root,
+          )
+        :
+          array(
+            '/x/y/z',
+            '/x/y',
+            '/x',
+            '/',
+          ),
       ),
 
     );
diff --git a/src/filesystem/__tests__/PhutilDeferredLogTestCase.php b/src/filesystem/__tests__/PhutilDeferredLogTestCase.php
--- a/src/filesystem/__tests__/PhutilDeferredLogTestCase.php
+++ b/src/filesystem/__tests__/PhutilDeferredLogTestCase.php
@@ -105,7 +105,7 @@
 
     $futures = array();
     for ($ii = 0; $ii < $n_writers; $ii++) {
-      $futures[] = new ExecFuture('%s %d %s', $bin, $n_lines, (string)$tmp);
+      $futures[] = new ExecFuture('php %s %d %s', $bin, $n_lines, (string)$tmp);
     }
 
     id(new FutureIterator($futures))
diff --git a/src/filesystem/__tests__/PhutilFileLockTestCase.php b/src/filesystem/__tests__/PhutilFileLockTestCase.php
--- a/src/filesystem/__tests__/PhutilFileLockTestCase.php
+++ b/src/filesystem/__tests__/PhutilFileLockTestCase.php
@@ -148,6 +148,12 @@
   }
 
   private function holdLock($file) {
+    if (phutil_is_windows()) {
+      // Skip since stdout is not reliable on Windows + PHP.
+      $this->assertSkipped(pht("This test doesn't work on Windows."));
+      return;
+    }
+
     $future = $this->buildLockFuture('--hold', $file);
 
     // We can't return until we're sure the subprocess has had time to acquire
@@ -174,9 +180,14 @@
     $root = dirname(phutil_get_library_root('phutil'));
     $bin = $root.'/scripts/utils/lock.php';
 
-    // NOTE: Use `exec` so this passes on Ubuntu, where the default `dash` shell
-    // will eat any kills we send during the tests.
-    $future = new ExecFuture('exec php %s %C %s', $bin, $flags, $file);
+    if (phutil_is_windows()) {
+      $future = new ExecFuture('php %s %C %s', $bin, $flags, $file);
+    } else {
+      // NOTE: Use `exec` so this passes on Ubuntu,
+      // where the default `dash` shell will eat any
+      // kills we send during the tests.
+      $future = new ExecFuture('exec php %s %C %s', $bin, $flags, $file);
+    }
     $future->start();
     return $future;
   }