This lecture covers the theory and practical examples of two-port circuits, focusing on phase shifters and attenuators. It explains the measurement of S-parameters, lossless and lossy circuits, and various types of phase shifters. The instructor demonstrates the design and operation of Fox' phase shifters, reciprocal and non-reciprocal phase shifters, and rotative blade attenuators. Additionally, the lecture discusses reactive and resistive attenuators, providing insights into impedance matrices and scattering parameter matrices for these devices.