Dynamic changes in the posttranslational modification of proteins govern most cellular signaling pathways. Work over the past decade has connected many of these processes with the covalent attachment of the small ubiquitin-like modifier (SUMO) protein to target proteins, but a global view of the dynamics of SUMOylation was missing. A system-level proteomics approach has now been used to describe quantitative changes in protein modification with the SUMO-2 paralog during the response to heat shock. The SUMOylation status of more than 700 proteins was monitored in HeLa cells during the induction of hyperthermic stress and the recovery period. A massive redistribution of SUMO-2 was observed that affected many biological pathways that are important for the heat shock response, including cell cycle regulation, transcription, translation, protein folding, and DNA repair. Collectively, these data suggest a wide-ranging role for SUMOylation in the cellular response to hyperthermic stress. The strategies that were developed to provide this global view of SUMOylation should guide future approaches to probing quantitative changes in protein modification.