This lecture discusses the linear response for large chaotic systems, focusing on naturally occurring systems with chaotic dynamics and physical steady states. Topics include SRB states, Lyapunov exponents, formal linear response formula, uniformly hyperbolic and non-uniformly hyperbolic dynamical systems, and the convergence of the linear response formula. The instructor presents a non-rigorous argument and analysis to support the convergence of the linear response formula. The lecture concludes by highlighting the existence of the derivative of an SRB state and the expectation of linear response in systems with large dimensions.