Laser is a device that amplifies the light produced due to stimulated emission of radiation and then emits light that is spatially and temporally coherent. Lasers operate in either pulsed mode or continuous mode. They are of various types, such as gas lasers, solid-state lasers, semiconductor lasers, dye lasers, fiber lasers, etc. These are used in laser printers, barcode scanners, optical disk drives, laser surgery, DNA sequencing, free-space optical communication, etc. This book outlines the processes and applications of lasers in detail. Such selected concepts that redefine this field have been presented herein. This book is meant for students who are looking for an elaborate reference on lasers.