Apart from a personal tragedy, could Down syndrome, cancer and infertility possibly have something in common? Are there links between a syndrome with physical and mental problems, a tumor growing out of control and the incapability to reproduce? These questions can be answered if we look at the biological functions of a protein complex, named cohesin, which is the main protagonist in the regulation of sister chromatid cohesion during chromosome segregation in cell division. The establishment, maintenance and removal of sister chromatid cohesion is one of the most fascinating and dangerous processes in the life of a cell. Errors in the control of sister chromatid cohesion frequently lead to cell death or aneuploidy. Recent results showed that cohesins also have important functions in non-dividing cells, revealing new, unexplored roles for these proteins in human syndromes, currently known as cohesinopathies. In the last 10 years, we have improved our understanding of the molecular mechanisms of the cohesin and cohesin-interacting proteins regulating the different events of sister chromatid cohesion during cell division in mitosis and meiosis.