This lecture delves into the behavior of real polymer chains, exploring concepts such as self-avoiding random walks, polymer conformation, effective interaction potentials, excluded volume, and the classification of solvents. It also covers the phase diagram of polymer solutions, the omnipresence of the A-state in polymer melts, and provides an outlook on end-to-end distance changes upon deformation. The instructor emphasizes the mapping of ideal chain models onto random walks and the accurate description of polymer melts and solution behavior.