diff --git a/gitflow-common b/gitflow-common
new file mode 100644
index 0000000..0cc6802
--- /dev/null
+++ b/gitflow-common
@@ -0,0 +1,148 @@
+#
+# git-flow -- A collection of Git extensions to provide high-level
+# repository operations for Vincent Driessen's branching model.
+#
+# Original blog post presenting this model is found at:
+#    http://nvie.com/archives/323
+#
+# Feel free to contribute to this project at:
+#    http://github.com/nvie/gitflow
+#
+# Copyright (c) 2010 by Vincent Driessen
+# Copyright (c) 2010 by Benedikt Böhm
+#
+
+# shell output
+warn() { echo "$@" >&2; }
+die() { warn "$@"; exit 1; }
+
+# set logic
+has() {
+	local item=$1; shift
+	echo " $@ " | grep -q " $item "
+}
+
+# basic math
+min() { [ "$1" -le "$2" ] && echo "$1" || echo "$2"; }
+max() { [ "$1" -ge "$2" ] && echo "$1" || echo "$2"; }
+
+# basic string matching
+startswith() { [ "$1" != "${1#$2}" ]; }
+endswith() { [ "$1" != "${1#$2}" ]; }
+
+# convenience functions for checking shFlags flags
+flag() { eval FLAG='$FLAGS_'$1; [ $FLAG -eq $FLAGS_TRUE ]; }
+noflag() { eval FLAG='$FLAGS_'$1; [ $FLAG -ne $FLAGS_TRUE ]; }
+
+#
+# Git specific common functionality
+#
+
+# get all available branches
+LOCAL_BRANCHES=$(git branch | sed 's/^[* ] //')
+REMOTE_BRANCHES=$(git branch -r | sed 's/^[* ] //')
+ALL_BRANCHES="$LOCAL_BRANCHES $REMOTE_BRANCHES"
+
+gitflow_test_clean_working_tree() {
+	if ! git diff --no-ext-diff --ignore-submodules --quiet --exit-code; then
+		return 1
+	elif ! git diff-index --cached --quiet --ignore-submodules HEAD --; then
+		return 2
+	else
+		return 0
+	fi
+}
+
+gitflow_require_clean_working_tree() {
+	gitflow_test_clean_working_tree
+	result=$?
+	if [ $result -eq 1 ]; then
+		die "fatal: Working tree contains unstaged changes. Aborting."
+	fi
+	if [ $result -eq 2 ]; then
+		die "fatal: Index contains uncommited changes. Aborting."
+	fi
+}
+
+gitflow_require_local_branch() {
+	if ! has $1 $LOCAL_BRANCHES; then
+		die "fatal: Local branch '$1' does not exist and is required."
+	fi
+}
+
+gitflow_require_remote_branch() {
+	if ! has $1 $REMOTE_BRANCHES; then
+		die "Remote branch '$1' does not exist and is required."
+	fi
+}
+
+gitflow_require_branch() {
+	if ! has $1 $ALL_BRANCHES; then
+		die "Branch '$1' does not exist and is required."
+	fi
+}
+
+gitflow_require_branch_absent() {
+	if has $1 $ALL_BRANCHES; then
+		die "Branch '$1' already exists. Pick another name."
+	fi
+}
+
+#
+# gitflow_test_branches_equal()
+#
+# Tests whether branches and their "origin" counterparts have diverged and need
+# merging first. It returns error codes to provide more detail, like so:
+#
+# 0    Branch heads point to the same commit
+# 1    First given branch needs fast-forwarding
+# 2    Second given branch needs fast-forwarding
+# 3    Branch needs a real merge
+#
+gitflow_test_branches_equal() {
+	commit1=$(git rev-parse "$1")
+	commit2=$(git rev-parse "$2")
+	if [ "$commit1" != "$commit2" ]; then
+		base=$(git merge-base "$commit1" "$commit2")
+		if [ "$commit1" = "$base" ]; then
+			return 1
+		elif [ "$commit2" = "$base" ]; then
+			return 2
+		else
+			return 3
+		fi
+	else
+		return 0
+	fi
+}
+
+gitflow_require_branches_equal() {
+	gitflow_require_local_branch "$1"
+	gitflow_require_remote_branch "$2"
+	gitflow_test_branches_equal "$1" "$2"
+	status=$?
+	if [ $status -gt 0 ]; then
+		warn "Branches '$1' and '$2' have diverged."
+		if [ $status -eq 1 ]; then
+			die "And branch '$1' may be fast-forwarded."
+		elif [ $status -eq 2 ]; then
+			# Warn here, since there is no harm in being ahead
+			warn "And local branch '$1' is ahead of '$2'."
+		else
+			die "Branches need merging first."
+		fi
+	fi
+}
+
+#
+# gitflow_is_branch_merged_into()
+#
+# Checks whether branch $1 is succesfully merged into $2
+#
+gitflow_is_branch_merged_into() {
+	local SUBJECT=$1
+	local BASE=$2
+	ALL_MERGES=$(git branch --contains $SUBJECT | sed 's/^[* ] //')
+	has $BASE $ALL_MERGES
+}
+