diff --git a/commit0/cli.py b/commit0/cli.py
index 8c82b08..c0d8596 100644
--- a/commit0/cli.py
+++ b/commit0/cli.py
@@ -10,6 +10,7 @@
 import commit0.harness.lint
 import commit0.harness.save
 from commit0.harness.constants import SPLIT, SPLIT_ALL
+from commit0.harness.utils import get_active_branch
 import subprocess
 import yaml
 import os
@@ -245,14 +246,13 @@ def test(
 
     commit0_config = read_commit0_dot_file(commit0_dot_file_path)
 
-    if not branch and not reference:
-        raise typer.BadParameter(
-            f"Invalid {highlight('BRANCH', Colors.RED)}. Either --reference or provide a branch name.",
-            param_hint="BRANCH",
-        )
     if reference:
         branch = "reference"
-    assert branch is not None, "branch is not specified"
+    if branch is None and not reference:
+        git_path = os.path.join(
+            commit0_config["base_dir"], repo_or_repo_path.split("/")[-1]
+        )
+        branch = get_active_branch(git_path)
 
     if verbose == 2:
         typer.echo(f"Running tests for repository: {repo_or_repo_path}")
@@ -264,7 +264,7 @@ def test(
         commit0_config["dataset_split"],
         commit0_config["base_dir"],
         repo_or_repo_path,
-        branch,
+        branch,  # type: ignore
         test_ids,
         backend,
         timeout,
@@ -294,14 +294,8 @@ def evaluate(
 ) -> None:
     """Evaluate Commit0 split you choose in Setup Stage."""
     check_commit0_path()
-    if not branch and not reference:
-        raise typer.BadParameter(
-            f"Invalid {highlight('BRANCH', Colors.RED)}. Either --reference or provide a branch name",
-            param_hint="BRANCH",
-        )
     if reference:
         branch = "reference"
-    assert branch is not None, "branch is not specified"
 
     commit0_config = read_commit0_dot_file(commit0_dot_file_path)
     check_valid(commit0_config["repo_split"], SPLIT)
diff --git a/commit0/harness/constants.py b/commit0/harness/constants.py
index f2957fa..9a92337 100644
--- a/commit0/harness/constants.py
+++ b/commit0/harness/constants.py
@@ -16,6 +16,8 @@ class Files(TypedDict):
     patch: Dict[str, Path]
 
 
+BASE_BRANCH = "commit0"
+
 # Constants - Evaluation Log Directories
 BASE_IMAGE_BUILD_DIR = Path("logs/build_images/base")
 REPO_IMAGE_BUILD_DIR = Path("logs/build_images/repo")
diff --git a/commit0/harness/evaluate.py b/commit0/harness/evaluate.py
index 11dbc98..ddc4b15 100644
--- a/commit0/harness/evaluate.py
+++ b/commit0/harness/evaluate.py
@@ -5,12 +5,12 @@
 from concurrent.futures import ThreadPoolExecutor, as_completed
 from datasets import load_dataset
 from tqdm import tqdm
-from typing import Iterator
+from typing import Iterator, Union
 
 from commit0.harness.run_pytest_ids import main as run_tests
 from commit0.harness.get_pytest_ids import main as get_tests
 from commit0.harness.constants import RepoInstance, SPLIT, RUN_PYTEST_LOG_DIR
-from commit0.harness.utils import get_hash_string
+from commit0.harness.utils import get_hash_string, get_active_branch
 
 logging.basicConfig(
     level=logging.INFO, format="%(asctime)s - %(name)s - %(levelname)s - %(message)s"
@@ -23,7 +23,7 @@ def main(
     dataset_split: str,
     repo_split: str,
     base_dir: str,
-    branch: str,
+    branch: Union[str, None],
     backend: str,
     timeout: int,
     num_cpus: int,
@@ -32,16 +32,19 @@ def main(
 ) -> None:
     dataset: Iterator[RepoInstance] = load_dataset(dataset_name, split=dataset_split)  # type: ignore
     repos = SPLIT[repo_split]
-    pairs = []
+    triples = []
     log_dirs = []
     for example in dataset:
         repo_name = example["repo"].split("/")[-1]
         if repo_split != "all" and repo_name not in SPLIT[repo_split]:
             continue
-        pairs.append((repo_name, example["test"]["test_dir"]))
         hashed_test_ids = get_hash_string(example["test"]["test_dir"])
+        if branch is None:
+            git_path = os.path.join(base_dir, repo_name)
+            branch = get_active_branch(git_path)
         log_dir = RUN_PYTEST_LOG_DIR / repo_name / branch / hashed_test_ids
         log_dirs.append(str(log_dir))
+        triples.append((repo_name, example["test"]["test_dir"], branch))
 
     with tqdm(total=len(repos), smoothing=0, desc="Evaluating repos") as pbar:
         with ThreadPoolExecutor(max_workers=num_workers) as executor:
@@ -61,7 +64,7 @@ def main(
                     rebuild_image=rebuild_image,
                     verbose=0,
                 ): None
-                for repo, test_dir in pairs
+                for repo, test_dir, branch in triples
             }
             # Wait for each future to complete
             for future in as_completed(futures):
diff --git a/commit0/harness/run_pytest_ids.py b/commit0/harness/run_pytest_ids.py
index 09fbe45..fd45080 100644
--- a/commit0/harness/run_pytest_ids.py
+++ b/commit0/harness/run_pytest_ids.py
@@ -82,15 +82,30 @@ def main(
             )
         except Exception as e:
             raise e
+    commit_id = ""
     if branch == "reference":
         commit_id = example["reference_commit"]
     else:
-        try:
-            local_repo.git.checkout(branch)
-            local_branch = local_repo.branches[branch]
-            commit_id = local_branch.commit.hexsha
-        except Exception as e:
-            raise Exception(f"Problem checking out branch {branch}.\n{e}")
+        # Check if it's a local branch
+        if branch in local_repo.branches:
+            commit_id = local_repo.commit(branch).hexsha
+        else:
+            found_remote_branch = False
+            for remote in local_repo.remotes:
+                remote.fetch()  # Fetch latest updates from each remote
+
+                # Check if the branch exists in this remote
+                for ref in remote.refs:
+                    if (
+                        ref.remote_head == branch
+                    ):  # Compare branch name without remote prefix
+                        commit_id = local_repo.commit(ref.name).hexsha
+                        found_remote_branch = True
+                        break  # Branch found, no need to keep checking this remote
+                if found_remote_branch:
+                    break  # Stop checking other remotes if branch is found
+            if not found_remote_branch:
+                raise Exception(f"Branch {branch} does not exist locally or remotely.")
     patch = generate_patch_between_commits(
         local_repo, example["base_commit"], commit_id
     )
diff --git a/commit0/harness/setup.py b/commit0/harness/setup.py
index edaadcd..b355572 100644
--- a/commit0/harness/setup.py
+++ b/commit0/harness/setup.py
@@ -7,7 +7,7 @@
 from commit0.harness.utils import (
     clone_repo,
 )
-from commit0.harness.constants import RepoInstance, SPLIT
+from commit0.harness.constants import BASE_BRANCH, RepoInstance, SPLIT
 
 
 logging.basicConfig(
@@ -29,7 +29,12 @@ def main(
             continue
         clone_url = f"https://github.com/{example['repo']}.git"
         clone_dir = os.path.abspath(os.path.join(base_dir, repo_name))
-        clone_repo(clone_url, clone_dir, example["base_commit"], logger)
+        branch = dataset_name.split("/")[-1]
+        repo = clone_repo(clone_url, clone_dir, branch, logger)
+        if BASE_BRANCH in repo.branches:
+            repo.git.branch("-d", BASE_BRANCH)
+        repo.git.checkout("-b", BASE_BRANCH)
+        logger.info("Checked out the base commit: commit 0")
 
 
 __all__ = []
diff --git a/commit0/harness/utils.py b/commit0/harness/utils.py
index 8836415..b006035 100644
--- a/commit0/harness/utils.py
+++ b/commit0/harness/utils.py
@@ -6,7 +6,7 @@
 import time
 import sys
 from pathlib import Path
-from typing import Optional
+from typing import Optional, Union
 
 from fastcore.net import HTTP404NotFoundError, HTTP403ForbiddenError  # type: ignore
 from ghapi.core import GhApi
@@ -85,7 +85,7 @@ def extract_test_output(ss: str, pattern: str) -> str:
 
 
 def clone_repo(
-    clone_url: str, clone_dir: str, commit: str, logger: logging.Logger
+    clone_url: str, clone_dir: str, branch: str, logger: logging.Logger
 ) -> git.Repo:
     """Clone repo into the specified directory if it does not already exist.
 
@@ -98,8 +98,8 @@ def clone_repo(
         URL of the repository to clone.
     clone_dir : str
         Directory where the repository will be cloned.
-    commit : str
-        The commit hash or branch/tag name to checkout.
+    branch : str
+        The branch/tag name to checkout.
     logger : logging.Logger
         The logger object.
 
@@ -129,11 +129,10 @@ def clone_repo(
         except git.exc.GitCommandError as e:
             raise RuntimeError(f"Failed to clone repository: {e}")
 
-    logger.info(f"Checking out {commit}")
     try:
-        repo.git.checkout(commit)
+        repo.git.checkout(branch)
     except git.exc.GitCommandError as e:
-        raise RuntimeError(f"Failed to check out {commit}: {e}")
+        raise RuntimeError(f"Failed to check out {branch}: {e}")
 
     return repo
 
@@ -190,4 +189,33 @@ def generate_patch_between_commits(
         raise Exception(f"Error generating patch: {e}")
 
 
+def get_active_branch(repo_path: Union[str, Path]) -> str:
+    """Retrieve the current active branch of a Git repository.
+
+    Args:
+    ----
+        repo_path (Path): The path to git repo.
+
+    Returns:
+    -------
+        str: The name of the active branch.
+
+    Raises:
+    ------
+        Exception: If the repository is in a detached HEAD state.
+
+    """
+    repo = git.Repo(repo_path)
+    try:
+        # Get the current active branch
+        branch = repo.active_branch.name
+    except TypeError as e:
+        raise Exception(
+            f"{e}\nThis means the repository is in a detached HEAD state. "
+            "To proceed, please specify a valid branch by using --branch {branch}."
+        )
+
+    return branch
+
+
 __all__ = []