E3 ligase ligand-linker conjugates 40 are primarily utilized in the field of targeted protein degradation, particularly in the development of PROTACs (Proteolysis Targeting Chimeras). These conjugates play a crucial role in bridging the E3 ubiquitin ligase and the target protein, facilitating the ubiquitination and subsequent degradation of the target protein via the proteasome pathway. This application is highly significant in drug discovery, especially for targeting proteins that are traditionally considered "undruggable," such as transcription factors or scaffold proteins. By enabling selective degradation, these conjugates offer a promising approach for treating various diseases, including cancer, neurodegenerative disorders, and autoimmune conditions. Their modular design allows for customization, enhancing specificity and efficacy in degrading disease-causing proteins.