Ubiquitin is a conserved eukaryotic protein essential to cellular survival. Although it contributes to various cellular processes including vesicular trafficking and signal transduction, it is primarily known for its role in protein homeostasis. Specifically, ubiquitin serves as a tag placed on unneeded cellular proteins that targets them for proteasomal degradation. After transcription and post-translational modification, ubiquitin monomers may become activated and conjugated to target proteins through the E1/E2/E3 enzymatic pathway. Multiple additional conjugations of ubiquitin monomers results in the creation of polyubiquitin chains, which signals the protein for degradation in the 26S proteasome. Here a review of this process, along with a number of ubiquitin's other roles, is presented.