Condensins are pentameric complexes that were initially described as being involved in the dynamics of chromosomes during mitosis. It has been recently established that two related complexes (Condensin I and Condensin II) contribute to this process. An increasing sum of studies, using different approaches in various organisms, leads to the paradigm that Condensins are required for the correct segregation of replicated chromosomes by cooperating somehow with Topoisomerase II in sister chromatid resolution. Depending on species and/or experimental studies, these complexes also contribute to some aspects of the assembly and compaction of mitotic chromosomes. Recent studies provided evidences that Condensins and related complexes also function in non-mitotic processes such as replication and transcription. Biochemical studies have highlighted mechanistic aspects of Condensin function and initiated a fine functional dissection of core and regulatory subunits. However, the exact contribution of each subunit remains largely elusive as well as the functional interplay between Condensin I and Condensin II.