How do I clone a single branch in Git?

Note: the git1.7.10 (April 2012) actually allows you to clone only one branch:

# clone only the remote primary HEAD (default: origin/master)
git clone <url> --single-branch

# as in:
git clone <url> --branch <branch> --single-branch [<folder>]

You can see it in t5500-fetch-pack.sh:

test_expect_success 'single branch clone' '
  git clone --single-branch "file://$(pwd)/." singlebranch
'

Tobu comments that:

This is implicit when doing a shallow clone.
This makes git clone --depth 1 the easiest way to save bandwidth.

And since Git 1.9.0 (February 2014), shallow clones support data transfer (push/pull), so that option is even more useful now.
See more at "Is git clone --depth 1 (shallow clone) more useful than it makes out?".

---

"Undoing" a shallow clone is detailed at "Convert shallow clone to full clone" (git 1.8.3+)

# unshallow the current branch
git fetch --unshallow

# for getting back all the branches (see Peter Cordes' comment)
git config remote.origin.fetch refs/heads/*:refs/remotes/origin/*
git fetch --unshallow

As Chris comments:

the magic line for getting missing branches to reverse --single-branch is (git v2.1.4):

git config remote.origin.fetch +refs/heads/*:refs/remotes/origin/*
git fetch --unshallow  

---

With Git 2.26 (Q1 2020), "git clone --recurse-submodules --single-branch" now uses the same single-branch option when cloning the submodules.

See commit 132f600, commit 4731957 (21 Feb 2020) by Emily Shaffer (nasamuffin).
^{(Merged by Junio C Hamano -- gitster -- in commit b22db26, 05 Mar 2020)}

clone: pass --single-branch during --recurse-submodules

^{Signed-off-by: Emily Shaffer
Acked-by: Jeff King}

Previously, performing "git clone --recurse-submodules --single-branch" resulted in submodules cloning all branches even though the superproject cloned only one branch.

Pipe --single-branch through the submodule helper framework to make it to 'clone' later on.

One way is to execute the following.

git clone user@git-server:project_name.git -b branch_name /your/folder

Where branch_name is the branch of your choice and "/your/folder" is the destination folder for that branch. It's true that this will bring other branches giving you the opportunity to merge back and forth.

Update

Now, starting with Git 1.7.10, you can now do this

git clone user@git-server:project_name.git -b branch_name --single-branch /your/folder

Using Git version 1.7.3.1 (on Windows), here's what I do ($BRANCH is the name of the branch I want to checkout and $REMOTE_REPO is the URL of the remote repository I want to clone from):

mkdir $BRANCH
cd $BRANCH
git init
git remote add -t $BRANCH -f origin $REMOTE_REPO
git checkout $BRANCH

The advantage of this approach is that subsequent git pull (or git fetch) calls will also just download the requested branch.