Past studies have consistently shown that firms favor past partners when forming new alliances. This behavior has been associated with a need to have knowledge of potential partners' capabilities and reliability. We consider inertia as an alternative rationale. Inertia and evaluation factors were tested in the context of underwriting syndicate formations in the U.S. investment banking industry. The results suggest both inertia and several evaluation criteria, including reciprocity, experience, and prior performance, influence partner selection.