Human chromosomes, if linearly stitched together, span a length of over 2 meters. They need to be properly folded to be housed in the cell nucleus with a diameter of 10 µm. Chromosome folding also occurs in a dynamic, structured way that regulates gene expression, and DNA replication and repair. Initially discovered as the molecular glue that holds sister chromatids for segregation, the cohesin complex has recently been shown to be critical for structured chromosome folding. Cohesin organizes the genome by a process termed loop extrusion. Recent progress on the mechanism and function of cohesin in genome organization will be discussed.