The Boehringer Ingelheim Fonds International Titisee Conference on Mechanisms of Cell Polarity took place between 12 and 16 March 2008, in Titisee, Germany, and was organized by A. Ridley and M. Peter. ![][1] See Glossary for abbreviations used in this article “Consider a spherical cow.” So goes the punchline of a well‐known joke told by and about theoretical physicists. The concept of a completely symmetric, spherical cell is as foreign to biologists as the spherical bovine is to farmers: the establishment and maintenance of polarity has a crucial role in the correct function of numerous cell types; even spherical bacteria exhibit polarity. The Ninety‐Seventh International Titisee Conference on Mechanisms of Cell Polarity brought together experts on diverse organisms and cell types to discuss general principles governing the establishment and maintenance of cell polarity. The mechanisms that are responsible for the localized positioning of the bacterial division machinery were discussed by J. Errington (Newcastle, UK) in Bacillus subtilis and by C. Jacobs‐Wagner (New Haven, USA) in Caulobacter crescentus . During cytokinesis of B. subtilis , cell‐wall growth is spatially restricted to a circular ring, which eventually becomes the division septum. The tubulin‐like bacterial protein, FtsZ, which is usually found in helical‐like structures, rearranges as a ring about the division plane where it recruits other proteins that are responsible for cell division (Cabeen & Jacobs‐Wagner, 2007). After cytokinesis, rod‐shaped bacteria elongate by localizing their growth either to cylindrical regions—for example, Escherichia coli and B. subtilis or—to the poles—for example, Corynebacterium . This polarized growth is partly regulated by the bacterial actin homologue MreB. These proteins—found only in non‐spherical bacteria—form helical filamentous structures that are involved directly in the control of cell‐shape. Elongation of B. subtilis requires the coordinated activity of MreB and its two homologues, Mbl and MreBH. MreB also has a role … [1]: /embed/graphic-1.gif