Cohesin is a chromosome-bound, multisubunit adenosine triphosphatase complex. 
After loading onto chromosomes, it generates loops to regulate chromosome 
functions. It has been suggested that cohesin organizes the genome through loop 
extrusion, but direct evidence is lacking. Here, we used single-molecule imaging 
to show that the recombinant human cohesin-NIPBL complex compacts both naked and 
nucleosome-bound DNA by extruding DNA loops. DNA compaction by cohesin requires 
adenosine triphosphate (ATP) hydrolysis and is force sensitive. This compaction 
is processive over tens of kilobases at an average rate of 0.5 kilobases per 
second. Compaction of double-tethered DNA suggests that a cohesin dimer extrudes 
DNA loops bidirectionally. Our results establish cohesin-NIPBL as an ATP-driven 
molecular machine capable of loop extrusion.