Microscopes have a specialized use in biological research and clinical diagnosis because they possess characteristics of magnification and resolving power. The capacity of microscope both to magnify and resolve depends on kind of illumination and type of lenses used. Compound light microscope permits gross examination of cellular structure and is an attractive tool for routine investigation in hospital lab. Information on its principle, components, use and limitations has been explained with illustrations. For special investigations scientists have designed microscopes with unique features, that is, phase contrast, interference, polarizing, ultraviolet, fluorescent and X-ray microscopes. Essential features of such special microscopes have been analysed in this chapter. The development of electron microscope has added a new dimension to the depth to which cells can be viewed. Knowledge of transmission, scanning and high voltage electron microscope has become essential for medical students. The details of these electron microscopes have been covered with illustrations. To complete the coverage of subject matter ultrastructures of plasma membrane, endoplasmic recticulum, mitochondria, Golgi complex, filaments and microtubules, lysosomes, nuclear envelope, nucleoli and chromatin have been included in this chapter. A brief note on scanning laser microscope has also been added.