Among the medicinally useful constituent of plants, the alkaloids constitute an important group. The accounts and discussions given here attempt to summarize (a) the plant sources and fundamental properties of the medicinally important alkaloids, (b) the principles and certain useful methods for their separation and isolation from plant materials, and (c) some aspects of their biosynthesis. They are intended as an introduction to these aspects of the study of alkaloids, as a supplement to the relevant sections on the alkaloids in standard text-books of pharmaceutical subjects, and to provide a collateral background for related laboratory works. It is hoped that these introductory accounts may also serve to prepare the student for proceeding to independent and effective use of the more comprehensive literature on these and other alkaloids.