UBI traps are used to isolate and identify ubiquitylated proteins from cells, tissues or organs. Multiple ubiquitin binding domains (UBDs) contribute to enhance their affinity for polyubiquitin chains compared to single UBD.  Prototype UBI traps interfere with the action of de-ubiquitylating enzymes (DUBs) and the proteasome which contribute to increase the yield of ubiquitylated proteins purified and facilitate the detection of low abundance proteins. These unique properties are not observed with any other technologies that can be used in a large panel of applications.