The more stringent environmental regulations enacted throughout the world have increased the need of more active hydrotreating (HDT) catalysts, in the petroleum refining industry. Usually, the catalysts used for diesel oil hydrotreatment are ?-Al2O3 supported molybdenum or tungsten sulfides promoted with cobalt or nickel. Current strategies for the design of novel HDS catalysts often include variations in the support formulation, catalyst preparation method and active phase formulation. In this sense, the new generations of catalysts, such as NEBULA®, are based on a totally different concept of bulk-like. In this chapter, we present recent research related to the synthesis, characterization and performance of trimetallic sulfide nanocatalysts for hydrodesulfurization. The present chapter analyses the state of art of the ternary sulfide hydrotreating catalysts.