This chapter describes the use of ureas and thioureas as organocatalysts in sustainable organic transformations. After a short overview of the factors that make these moieties so attractive to be incorporated in a catalyst scaffold, the rest of the chapter categorises the ureas and thioureas depending on the structural elements of each catalyst. Monofunctional (thio)ureas, tertiary amine-(thio)ureas, primary amine-(thio)ureas, secondary amine-(thio)ureas and miscellaneous (thio)urea examples are discussed. Each of these categories are fully presented, focusing on the first examples in the literature, the most important classes of catalyst among each subclass, and, the main focus of this chapter, transformations that are sustainable. Thus, catalytic examples that utilise low catalyst-loadings, low reagent ratios, and short reaction times are highlighted, with the intent that these type of processes can potentially find applications in chemical industry.