Bacterial cytokinesis depends upon the tubulin-like GTPase FtsZ, which 
polymerizes into an annular structure at midcell (the Z-ring) that defines the 
division site. The Z-ring nucleates assembly of downstream machinery required 
for cell wall synthesis and membrane fission, but may also generate constrictive 
force. Recent high-resolution imaging of FtsZ in vivo has begun to illuminate 
the organization of filaments within the Z-ring. This in vivo work has been 
complemented by reconstitution of Z-rings in vitro to demonstrate the 
force-generating capacity of FtsZ and explore its mechanism of action. Despite 
these technical advances, whether FtsZ-mediated force generation is required for 
cytokinesis and how Z-ring structure and constriction are mechanistically linked 
to cell wall remodeling are open questions.