diff --git a/.gitignore b/.gitignore
index 7626168a..70ca3865 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,6 +13,7 @@ data8assets/
 .autopull_list
 summer/
 test-repo/
+venv/
 
 .ipynb_checkpoints
 docs/_build
\ No newline at end of file
diff --git a/nbgitpuller/handlers.py b/nbgitpuller/handlers.py
index 289f7228..f83ad7d5 100644
--- a/nbgitpuller/handlers.py
+++ b/nbgitpuller/handlers.py
@@ -52,7 +52,7 @@ def get(self):
 
         try:
             repo = self.get_argument('repo')
-            branch = self.get_argument('branch')
+            branch = self.get_argument('branch', None)
             depth = self.get_argument('depth', None)
             if depth:
                 depth = int(depth)
@@ -73,7 +73,7 @@ def get(self):
             self.set_header('content-type', 'text/event-stream')
             self.set_header('cache-control', 'no-cache')
 
-            gp = GitPuller(repo, branch, repo_dir, depth=depth, parent=self.settings['nbapp'])
+            gp = GitPuller(repo, repo_dir, branch=branch, depth=depth, parent=self.settings['nbapp'])
 
             q = Queue()
 
@@ -149,7 +149,7 @@ def get(self):
         app_env = os.getenv('NBGITPULLER_APP', default='notebook')
 
         repo = self.get_argument('repo')
-        branch = self.get_argument('branch', 'master')
+        branch = self.get_argument('branch', None)
         depth = self.get_argument('depth', None)
         urlPath = self.get_argument('urlpath', None) or \
                   self.get_argument('urlPath', None)
diff --git a/nbgitpuller/pull.py b/nbgitpuller/pull.py
index 369c4292..f64b18e3 100644
--- a/nbgitpuller/pull.py
+++ b/nbgitpuller/pull.py
@@ -66,15 +66,75 @@ def _depth_default(self):
         where the GitPuller class hadn't been loaded already."""
         return int(os.environ.get('NBGITPULLER_DEPTH', 1))
 
-    def __init__(self, git_url, branch_name, repo_dir, **kwargs):
-        assert git_url and branch_name
+    def __init__(self, git_url, repo_dir, **kwargs):
+        assert git_url
 
         self.git_url = git_url
-        self.branch_name = branch_name
+        self.branch_name = kwargs.pop("branch")
+
+        if self.branch_name is None:
+            self.branch_name = self.resolve_default_branch()
+        elif not self.branch_exists(self.branch_name):
+            raise ValueError(f"Branch: {self.branch_name} -- not found in repo: {self.git_url}")
+
         self.repo_dir = repo_dir
         newargs = {k: v for k, v in kwargs.items() if v is not None}
         super(GitPuller, self).__init__(**newargs)
 
+    def branch_exists(self, branch):
+        """
+        This checks to make sure the branch we are told to access
+        exists in the repo
+        """
+        try:
+            heads = subprocess.run(
+                ["git", "ls-remote", "--heads", self.git_url],
+                capture_output=True,
+                text=True,
+                check=True
+            )
+            tags = subprocess.run(
+                ["git", "ls-remote", "--tags", self.git_url],
+                capture_output=True,
+                text=True,
+                check=True
+            )
+            lines = heads.stdout.splitlines() + tags.stdout.splitlines()
+            branches = []
+            for line in lines:
+                _, ref = line.split()
+                refs, heads, branch_name = ref.split("/", 2)
+                branches.append(branch_name)
+            return branch in branches
+        except subprocess.CalledProcessError:
+            m = f"Problem accessing list of branches and/or tags: {self.git_url}"
+            logging.exception(m)
+            raise ValueError(m)
+
+    def resolve_default_branch(self):
+        """
+        This will resolve the default branch of the repo in
+        the case where the branch given does not exist
+        """
+        try:
+            head_branch = subprocess.run(
+                ["git", "ls-remote", "--symref", self.git_url, "HEAD"],
+                capture_output=True,
+                text=True,
+                check=True
+            )
+            for line in head_branch.stdout.splitlines():
+                if line.startswith("ref:"):
+                    # line resembles --> ref: refs/heads/main HEAD
+                    _, ref, head = line.split()
+                    refs, heads, branch_name = ref.split("/", 2)
+                    return branch_name
+            raise ValueError(f"default branch not found in {self.git_url}")
+        except subprocess.CalledProcessError:
+            m = f"Problem accessing HEAD branch: {self.git_url}"
+            logging.exception(m)
+            raise ValueError(m)
+
     def pull(self):
         """
         Pull selected repo from a remote git repository,
@@ -243,13 +303,11 @@ def main():
 
     parser = argparse.ArgumentParser(description='Synchronizes a github repository with a local repository.')
     parser.add_argument('git_url', help='Url of the repo to sync')
-    parser.add_argument('branch_name', default='master', help='Branch of repo to sync', nargs='?')
     parser.add_argument('repo_dir', default='.', help='Path to clone repo under', nargs='?')
     args = parser.parse_args()
 
     for line in GitPuller(
         args.git_url,
-        args.branch_name,
         args.repo_dir
     ).pull():
         print(line)
diff --git a/nbgitpuller/static/index.js b/nbgitpuller/static/index.js
index 53cd0cc0..c85d5897 100644
--- a/nbgitpuller/static/index.js
+++ b/nbgitpuller/static/index.js
@@ -44,12 +44,14 @@ require([
         // Start git pulling handled by SyncHandler, declared in handlers.py
         var syncUrlParams = {
             repo: this.repo,
-            branch: this.branch,
             targetpath: this.targetpath
         }
         if (typeof this.depth !== 'undefined' && this.depth != undefined) {
             syncUrlParams['depth'] = this.depth;
         }
+        if (typeof this.branch !== 'undefined' && this.branch != undefined) {
+            syncUrlParams['branch'] = this.branch;
+        }
         var syncUrl = this.baseUrl + 'git-pull/api?' + $.param(syncUrlParams);
 
         this.eventSource = new EventSource(syncUrl);
diff --git a/nbgitpuller/templates/status.html b/nbgitpuller/templates/status.html
index b20a7b7f..1fcd00dc 100644
--- a/nbgitpuller/templates/status.html
+++ b/nbgitpuller/templates/status.html
@@ -5,7 +5,7 @@
 data-base-url="{{ base_url | urlencode }}"
 data-repo="{{ repo | urlencode }}"
 data-path="{{ path | urlencode }}"
-data-branch="{{ branch | urlencode }}"
+{% if branch %}data-branch="{{ branch | urlencode }}"{% endif %}
 {% if depth %}data-depth="{{ depth | urlencode }}"{% endif %}
 data-targetpath="{{ targetpath | urlencode }}"
 {% endblock %}
diff --git a/tests/test_gitpuller.py b/tests/test_gitpuller.py
index c336ef06..05c01354 100644
--- a/tests/test_gitpuller.py
+++ b/tests/test_gitpuller.py
@@ -61,10 +61,10 @@ def push_file(self, path, content):
 
 
 class Puller(Repository):
-    def __init__(self, remote, path='puller', *args, **kwargs):
+    def __init__(self, remote, path='puller', branch="master", *args, **kwargs):
         super().__init__(path)
         remotepath = "file://%s" % os.path.abspath(remote.path)
-        self.gp = GitPuller(remotepath, 'master', path, *args, **kwargs)
+        self.gp = GitPuller(remotepath, path, branch=branch, *args, **kwargs)
 
     def pull_all(self):
         for line in self.gp.pull():
@@ -96,6 +96,47 @@ def test_initialize():
             assert puller.git('rev-parse', 'HEAD') == pusher.git('rev-parse', 'HEAD')
 
 
+def test_branch_exists():
+    with Remote() as remote, Pusher(remote) as pusher:
+        pusher.push_file('README.md', '1')
+        with Puller(remote, 'puller') as puller:
+            assert not puller.gp.branch_exists("wrong")
+            assert puller.gp.branch_exists("master")
+
+
+def test_exception_branch_exists():
+    with Remote() as remote, Pusher(remote) as pusher:
+        pusher.push_file('README.md', '1')
+        with Puller(remote, 'puller') as puller:
+            orig_url = puller.gp.git_url
+            puller.gp.git_url = ""
+            try:
+                puller.gp.branch_exists("wrong")
+            except Exception as e:
+                assert type(e) == ValueError
+            puller.gp.git_url = orig_url
+
+
+def test_resolve_default_branch():
+    with Remote() as remote, Pusher(remote) as pusher:
+        pusher.push_file('README.md', '1')
+        with Puller(remote, 'puller') as puller:
+            assert puller.gp.resolve_default_branch() == "master"
+
+
+def test_exception_resolve_default_branch():
+    with Remote() as remote, Pusher(remote) as pusher:
+        pusher.push_file('README.md', '1')
+        with Puller(remote, 'puller') as puller:
+            orig_url = puller.gp.git_url
+            puller.gp.git_url = ""
+            try:
+                puller.gp.resolve_default_branch()
+            except Exception as e:
+                assert type(e) == ValueError
+            puller.gp.git_url = orig_url
+
+
 def test_simple_push_pull():
     """
     Test the 'happy path' push/pull interaction