Many critical cellular functions, such as cell division and internal transport in vesicles (“vesicular trafficking”) require cell membranes to change shape. In a viral infection, the virus also must cause previously flat portions of the membrane to form small pouches (“buds”) filled with virus that then detach from the membrane and travel to infect another cell. Most such shape changes are facilitated by proteins interacting with the cell membrane. In this talk, I will describe some of the physical models for how these shape changes are accomplished, as well as two experimental techniques for testing those models, and report work in progress toward understanding this process for influenza virus budding.