The septin family is a conserved GTP-binding protein family and was originally discovered through genetic screening for budding yeast mutants. Septins are implicated in many cellular processes in fungi and metazoa. The function of septins usually depends on septin assembling into oligomeric complexes and highly ordered polymers. The expansion of the septin gene number in vertebrates increased the complex diversity of septins. In this review, we first discuss the evolution, structures and assembly of septin proteins in yeast and metazoa. Then, we review the function of septin proteins in cytokinesis, membrane remodeling and compartmentalization.