The book is divided into 8 chapters; first chapters is related to Fermat's principle and general theory of image formation in which sign convention, Abbe's sine condition, cardinal points of thin and thick lenses are described. Second chapter give an idea about different types of aberration produced in images and eye pieces used in optical instruments. Third chapter is related to interferometer of light in which Newton's ring experiment and different types of interferometer like Michelson's Fabry - Perot etc.; and their applications are described in systematic manner. Fourth, fifth ans sixth chapters are for diffraction of light showing Fresnel's and Fraunhofer class of diffraction, resolving and dispersive power of optical instruments. In this section diffraction due to N slits, means diffraction due to grating are also explained. Chapter seven is related to laser transition covering the knowledge of Ruby and He - Ne laser and application of laser, and chapter eight an idea about non-linear optics, holography and optical fibre.