This study attempts to systematically review the coherence, amplification and quantum effects of semiconductor lasers. The first section is concerned with the application of semiconductor lasers for coherent communication and spectroscopy. This is followed by a section which treats a semiconductor laser amplifier. The Fabry-Perot cavity amplifier, travelling-wave amplifier and injection lock oscillator are described. The third and final section of the text examines the quantum effects of semiconductor lasers. Squeezed state generation and the inhibition of spontaneous emission in semiconductor lasers are described as well as general quantum noise properties.