Localization of transmitters and receiving sensors is achieved by measuring radiation emitted by a source to a set of sensors, which are either on a definite pattern, known as an array, or one randomly located at irregular points, known as a distributed sensor array. This book discusses how to determine the position of sensors and transmit information to a central node, also known as the anchor node. Time of arrival, time difference of arrival, frequency time of arrival, and strength of received signal are also covered. The reader will learn effective algorithms and implementation, as well as numerical examples, with the inclusion of lab experiments. It discusses time synchronization, including the rotating laser beam to measure distance, in detail.