This lecture covers the design problem of filters, where requirements such as frequency response, phase, and computational resources are given to determine the filter coefficients. Practical limitations, the importance of transition bands, and the trade-offs between filter order and error tolerances are discussed. The lecture also explains why a flat response is unattainable and introduces equiripple error. The pros and cons of IIR and FIR filters are compared, highlighting their computational efficiency, stability, and design challenges. Different design methods for IIR and FIR filters are presented, emphasizing established techniques based on analog design and optimal minimax filter design.