Explore the intricacies of Single Spin Asymmetries and Transverse Momentum Dependent parton distribution functions (TMDs) in this fourth lecture by Andrea Signori. Delve into advanced topics in hadron structure and spin physics, crucial for understanding the upcoming Electron-Ion Collider (EIC) experiments. Learn how these concepts contribute to unraveling the internal structure of protons and neutrons, including quark and gluon distributions, nucleon mass composition, and spin origins. Gain insights into the frontier areas of EIC physics, preparing you for cutting-edge research in particle physics, QCD, hadron physics, and heavy ion physics. This 58-minute lecture is part of the International School and Workshop on Probing Hadron Structure at the Electron-Ion Collider, organized by the International Centre for Theoretical Sciences.