Faithful chromosome segregation in mitosis and meiosis requires the presence of the sister chromatid cohesion complex. The complex, which was initially identified and characterized in yeast Saccharomyces cerevisiae, and subsequently detected in other Eukaryota, is composed of four evolutionarily conserved core subunits (cohesins) Smc1, Smc3, Scc1/Mcd1 and Irr1/Scc3. Apart from the core proteins, accurate segregation requires also elements necessary for the deposition of cohesins and for the establishment and the regulation of cohesion. There are several models of cohesin structure and functioning. The oldest and the most popular ring model is currently replaced by the handcuff model. Regulation of cohesion is not very well established but the regulatory role of the Ecol, Irr1--STAG2, Pds5 and Wap1/Rad61 proteins seems undoubted. Meiotic cohesion differs from cohesion in mitosis and requires the specific Rec8 and Sgol proteins. Apart from the main function--the participation in chromosome segregation--cohesins are also involved in the regulation of transcription, DNA double-strand break repair and chromosome morphogenesis. Here we characterize elements of the complex, and describe models of the complex functioning. Moreover, we discuss the regulation of sister chromatid cohesion in mitosis and meiosis and, additionally, we describe atypical functions of cohesins.