The ubiquitin-proteasome system (UPS) plays a key role in protein quality control by breaking down misfolded, damaged, or excess proteins to maintain cellular proteostasis. Working alongside molecular chaperones such as Hsp70, Hsp90, and small heat shock proteins, the UPS helps manage protein equilibrium within cells. Chaperones recognize and bind unfolded or aggregated proteins, preventing harmful interactions and guiding them to the UPS for degradation. During cellular stress, when protein misfolding and aggregation intensify, this collaboration is crucial. Chaperones identify damaged proteins and may stabilize or refold them; if refolding fails, they recruit E3 ubiquitin ligases to tag these proteins with ubiquitin, marking them for proteasomal degradation. In neurodegenerative diseases, where protein aggregation is common, the UPS–chaperone interaction is essential for preventing proteotoxicity. However, persistent aggregation can overwhelm the UPS, compromising the cell’s health. Enhancing this mechanism may offer therapeutic strategies for diseases characterized by protein aggregation. Understanding the exact mechanisms of chaperone–UPS cooperation is vital for advancing therapies and insights into quality regulation of cellular proteins.