This work summarizes the historical progression of the field of lithium (Li) isotope studies and provides a comprehensive yet succinct overview of the research applications toward which they have been directed. In synthesizing the historical and current research, the volume also suggests prospective future directions of study. Not even a full decade has passed since the publication of a broadly inclusive summary of Li isotope research around the globe (Tomascak, 2004). In this short time, the use of this isotope system in the investigation of geo- and cosmochemical questions has increased dramatically, due, in part, to the advent of new analytical technology at the end of the last millennium. Lithium, as a light element that forms low-charge, moderate-sized ions, manifests a number of chemical properties that make its stable isotope system useful in a wide array of geo- and cosmochemical research fields.