As a matter of fact, synthetic nanomaterials have been widely employed in a variety of chemistry applications that include catalysis, photonics, electronics, photography, sensing, and information storage, among others. This special issue is dedicated for unprecedented papers that present innovative and relevant experimental studies and reviews focused on the synthesis, characterization, and application of well-defined nanomaterials for chemical applications, which is being demonstrated to be a very important topic with many groups working on it every year with expressive increasing in the past few years. As the properties of all nanomaterials are strongly dependent on their physical/chemical parameters, strategies for their controlled synthesis and the understanding of performance relationships have gained attention. In this issue, we would like to present developments on well-defined nanoparticles focusing on relationships between performance and physical/chemical features, such as shape, composition, size, hollow interiors, surface morphology, preferential facet exposition, which opens further possibilities for performance optimization. In this context, papers discussing the synthesis of well-defined nanomaterials correlating different physicochemical properties and the performances (conversion, selectivity, stability, and recyclability) on chemical transformations are welcome.