An astounding number of important regulatory and structural proteins are subject to modification by the attachment of ubiquitin or ubiquitin-like proteins. This modification acts as a targeting signal, delivering the modified protein to different locations in the cell and modifying its activity, macromolecular interactions, or half-life. Deubiquitination, or the removal of this modification, is being recognized as an important regulatory strategy. This reaction is catalyzed by processing proteases known as deubiquitinating enzymes (DUBs). More than 60 DUBs are already known, although little is known about their biological roles. This review concentrates on recent findings and new insights into this fascinating class of enzymes.