Developed as an introductory course, this up-to-date text discusses the major building blocks of present-day fiber-optic systems and presents their use in communications and sensing. Starting with easy-to-understand ray propagation in optical fibers, the book progresses towards the more complex topics of wave propagation in planar and cylindrical waveguides. Special emphasis has been given to the treatment of single-mode fibers the backbone of present-day optical communication systems. It also offers a detailed treatment of the theory behind optoelectronic sources (LEDs and injection laser diodes), detectors, modulators, and optical amplifiers. Contemporary in terms of technology, it presents topics such as erbium-doped fiber amplifiers (EDFAs) and wavelength-division multiplexing (WDM) along with dense WDM. Building upon these fundamental principles, the book introduces the reader to system design considerations for analog and digital fiber-optic communications. Emphasis ha s also been given to fiber-optic sensors and laser-based systems along with their industrial and other applications. This student-friendly text would be very useful to undergraduate students pursuing instrumentation, electronics, and communication engineering. It would also prove to be a good text for postgraduate students of physics.