The function of the GTPase dynamin has been discussed for several years. It clearly plays a role in vesicle budding, but, despite recent insights, precisely how it functions in this process is still a matter of debate. In addition, it is now clear that dynamin is a member of a large protein family, present in a variety of cellular locations where members apparently perform a range of functions. This article describes current understanding of the structure and function of the various dynamin family members.