Synopsis The present title introduce the sciences of immunology to provide a comprehensive over view of basic immunology that could serve either as a text book for introductory courses or as a concise, state-of-the-art review for practicing physicians and scientists from immunology and other related fields. It covers molecular and cell biology of defence mechanisms in health and diseases. Efforts have also been made to make the presentation lucid and accessible for beginning students, emphasizing major concepts while in corporating the latest experimental findings and theories throughout. The most important theories are presented at an increasing level of detail in successive chapters.