This text describes the interactions of light and the specimen in the microscope in relation to the manner in which they are used to generate contrast in the image of a specimen. Chapters cover bright-field and dark-ground techniques for both transmitted and reflected light, as well as the effects of the refractive index of the mounting medium surrounding the specimen. Subsequent chapters deal with the use of polarized light, phase and modulation contrast, interference and fluorescence and contrast technique outside the microscope.