Copper sulfide describes a group of chemical compounds consisting of copper and sulfur that can exist in various compositions. The properties of copper sulfide depend on the composition, size and shape of the material, making it an interesting candidate for various applications, including catalysis. The first part of this thesis describes several methods to prepare copper sulfide nanoparticles. Colloidal copper sulfide (hetero)nanocrystals as well as supported copper sulfide nanoparticles were prepared with good control over size, shape and composition. In addition, the methods resulted in copper sulfide nanoparticles suitable for catalytic applications by for example, removing bulky organic ligands from the particle surface to make the surface accessible for reactants, or by preparing nanoparticles anchored on a support material to improve their stability and handling. The second part of the thesis focusses on the applications of copper sulfide nanoparticles in photo- and electrocatalysis. From our findings, Cu2-xS nanoparticles are not very promising photocatalysts. However, their use in electrochemical CO2 reduction led to interesting results. Even though the copper sulfide nanoparticles reduce to metallic copper under typical CO2 and H+ reduction conditions, residual sulfur in the catalysts steered the product selectivity to formate.