This review of true time delay-based beamforming techniques includes analogue passive and active delay approaches with a rigorous analysis of performance considerations and limitations. An introduction to phase-shifter architectures illustrates performance degradation for high bandwidths due to frequency-dependent phase shift such as beam squinting and gain variation. True time delay-based approaches have the advantage of frequency-independent delay and readily find application in high data rate mm-wave networks. Tuned LC transmission lines, n-stage transmission line switching, trombone, and passive and active all-pass filter techniques are compared. Several practical nonideal implementations of timed antenna arrays are evaluated.