Coupled phase locked loops : stability synchronization chaos and communication with chaos Modern technological biological and socioeconomic systems are extremely complex. The study of such systems largely relies on the concepts of competition and cooperation (synchronization). The main approaches to the study of nonlinear dynamics of complex systems are now associated with models of collective dynamics of networks and ensembles formed by interacting dynamical elements. Unfortunately the applicability of analytical and qualitative methods of nonlinear dynamics to such complex systems is severely restricted due to the high dimension of phase space. Therefore studying the simplest models of networks which are ensembles with a small number of elements becomes of particular interest. Such models allow to make use of the entire spectrum of analytical qualitative and numerical methods of nonlinear dynamics. This book is devoted to the investigation of a kind of such systems namely small ensembles of coupled phase controlled oscillators. Authors address both traditional issues like synchronization that are relevant for applications in radio communications radio location energy etc. and nontraditional issues of excitation of chaotic oscillations and their possible application in advanced communication systems Introduction. Dynamical chaos and information communication Nonlinear dynamics of the phase system Cascade coupling of two phase systems Three cascade coupled phase system dynamics Phase systems parallel coupling Synchronization of chaotic oscillations Communication with chaos