Metal and metal sulfide clusters embedded in polymeric matrices represents a novel nanostructured material class. These materials combine optical transparency to magnetism, luminescence, UV-visible absorption, thermochromism, etc. leaving to unique functional materials that can be conveniently exploited for a number of applications in different technological fields. A really effective synthesis route for these materials is represented by the thermal decomposition of mercaptide molecules dissolved in polymer. Mercaptides can be dissolved/dispersed in polymers and thermally degraded at temperatures compatible with polymer stability (100°-250°C), generating metal atoms or metal sulfide molecules that leave to very small nanoparticles by clustering. Mercaptide synthesis, blending with polymers, and thermal decomposition are quite simple and general operations, consequently this approach can be easily applied for the preparation of a variety of nanocomposite systems. In this review, we present some fundamental aspects related to the chemistry of mercaptides (synthesis), the calorimetric study of their thermolysis process, the main techniques for nanocomposite characterization, and a short description of material applications. This article also includes recent patent coverage.