Tail‐anchored proteins form a distinct class of membrane proteins that have a single membrane anchor sequence at their C‐terminus, the tail‐anchor. Their N‐terminal portion is exposed to the cytosol. We have studied the roles of tail‐anchor domains of proteins residing in the mitochondrial outer membrane. Four distinct functions of the tail‐anchor domain were identified. First, the domain mediates the targeting to mitochondria in a process that probably requires a net positive charge at the C‐terminally flanking segment. Second, tail‐anchor domains facilitate the insertion into the mitochondrial outer membrane. Third, the tail‐anchor is responsible for the assembly of the respective protein into functional multi‐subunit complexes; and fourth, tail‐anchor domains can stabilize such complexes.