Abstract
The actin cytoskeleton is constantly assembling and disassembling. Cells harness the energy of these turnover dynamics to drive cell motility and organize cytoplasm. Although much is known about how cells control actin polymerization, we do not understand how actin filaments depolymerize inside cells. I briefly describe how the combination of imaging actin filament dynamics in cells and using in vitro biochemistry progressively altered our views of actin depolymerization. I describe why I do not think that the prevailing model of actin filament turnover--cofilin-mediated actin filament severing--can account for actin filament disassembly detected in cells. Finally, I speculate that cells might be able to tune the mechanism of actin depolymerization to meet physiological demands and selectively control the stabilities of different actin arrays.