This article reviews recent developments, contemporary design approaches and performance of nonmultilayer planar crossovers. These nonmultilayer crossover structures are useful for transmission and isolation of multiple signals in different orientations on the same side of a multilayer PCB to reduce complexity and cost, reduce the number of layers in the PCB, improve heat dissipation and reduce crosstalk. The article begins with an explanation of basic principles and the Butler matrix, and compares performance of different microstrip crossover structures in numerous applications. Monoband, dual-band, patch crossovers and filtering crossovers with microstrip rings and SIW cavities resonators are all explored in depth.