Reinforcement Learning: An Introduction, Richard S. Sutton and Andrew G. Barto, 2018 (The MIT Press) - The authoritative textbook for reinforcement learning. Chapters 9 and 10 provide foundational coverage of function approximation, including linear methods for value function approximation and common feature construction techniques.
Neuro-Dynamic Programming, Dimitri P. Bertsekas and John N. Tsitsiklis, 1996 (Athena Scientific) - A foundational book in the field of approximate dynamic programming, offering theoretical insights into function approximation, including linear methods and their convergence properties, relevant for understanding the stability of RL algorithms.