Ubiquitin is a highly conserved 76 amino acid polypeptide, which is covalently attached to target proteins to signal their degradation by the 26S proteasome or to modify their function or localization. Regulated protein degradation, which is associated with many dynamic cellular processes, occurs predominantly via the ubiquitin-proteasome system. Ubiquitin is conjugated to target proteins through the sequential actions of a ubiquitin-activating enzyme, ubiquitin-conjugating enzymes, and ubiquitin-protein ligases. The nematode Caenorhabditis elegans has one ubiquitin-activating enzyme, twenty putative ubiquitin-conjugating enzymes, and potentially hundreds of ubiquitin-protein ligases. Research in C. elegans has focused on the cellular functions of ubiquitin pathway components in the context of organismal development. A combination of forward genetics, reverse genetics, and genome-wide RNAi screens has provided information on the loss-of-function phenotypes for the majority of C. elegans ubiquitin pathway components. Additionally, detailed analysis of several classes of ubiquitin-protein ligases has led to the identification of their substrates and the molecular pathways that they regulate. This review presents a comprehensive overview of ubiquitin-mediated pathways in C. elegans with a description of the known components and their identified molecular, cellular, and developmental functions.