Fast new product development (NPD) is a top priority in rapidly changing markets. Improvisation, a form of unplanned action in which composition and execution converge in time, has emerged as a competence for accelerating NPD in face of uncertainty. Yet, research has failed to explore this potential. To fill in this void, we seek to explore how various types of team expertise shape the speed outcomes of improvisation in NPD. Specifically, we explore the moderating role of expertise diversity, declarative expertise, and transactive expertise. The results of a survey of NPD projects from 118 manufacturing firms show that expertise diversity and declarative expertise weaken while transactive memory strengthens the impact of improvisation on new product speed.