How can I see which Git branches are tracking which remote / upstream branch?

Very much a porcelain command, not good if you want this for scripting:

git branch -vv   # doubly verbose!

Note that with git 1.8.3, that upstream branch is displayed in blue (see "What is this branch tracking (if anything) in git?")

If you want clean output, see arcresu's answer - it uses a porcelain command that I don't believe existed at the time I originally wrote this answer, so it's a bit more concise and works with branches configured for rebase, not just merge.

git remote show origin

Replace 'origin' with whatever the name of your remote is.

If you look at the man page for git-rev-parse, you'll see the following syntax is described:

<branchname>@{upstream}, e.g. master@{upstream}, @{u}

The suffix @{upstream} to a branchname (short form <branchname>@{u}) refers to the branch that the branch specified by branchname is set to build on top of. A missing branchname defaults to the current one.

Hence to find the upstream of the branch master, you would do:

git rev-parse --abbrev-ref master@{upstream}
# => origin/master

To print out the information for each branch, you could do something like:

while read branch; do
  upstream=$(git rev-parse --abbrev-ref $branch@{upstream} 2>/dev/null)
  if [[ $? == 0 ]]; then
    echo $branch tracks $upstream
  else
    echo $branch has no upstream configured
  fi
done < <(git for-each-ref --format='%(refname:short)' refs/heads/*)

# Output:
# master tracks origin/master
# ...

This is cleaner than parsing refs and config manually.