Rho-family GTPases, such as RhoA, Rac1 and Cdc42, are molecular switches that regulate processes including cell proliferation, cytoskeletal reorganization and cell migration. The past few years have seen immense progress in our understanding of the numerous roles of these proteins and in the development of techniques for examining them. Three Commentaries in this issue of JCS examine recent advances. On p. 1291, Sandrine Etienne-Manneville tackles Cdc42. Cdc42 appears to be central to control of cell polarity, and studies in yeast and higher eukaryotes have revealed details of its upstream activators, downstream effectors and the ultimate targets of Cdc42 signalling. Meanwhile, leaps forward in imaging have enabled researchers to develop fluorescent probes that can non-invasively monitor when and where Rho GTPases are active in cells. On p. 1313, Olivier Pertz and Klaus Hahn discuss the design of such biosensors, which take advantage of the numerous GFP variants available and ever more cunning fluorescence resonance energy transfer (FRET) strategies. Finally, on p. 1301, Krister Wennerberg and Channing Der remind us that it is not just RhoA, Rac1 and Cdc42: there are at least 25 Rho proteins. And although some may have functions resembling those of their more well known siblings, others, such as Rnd, might not even depend on GTP/GDP cycling.