Metal oxide nanoparticles are a key component of functional materials, leading to novel Applications and improving the material properties in the fields of ceramics, catalysts, and electronic devices. To fulfill the increasing demand for nanoparticles, new processes such as the nonaqueous sol-gel synthe- sis are necessary that are feasible to fabricate highly crystalline nanoparticles with defined properties at larger scales. However, it requires a thorough knowledge of the chemical mechanisms and particle formation kinetics to understand the complex interdependence between process conditions and the final nanoparticle properties.  Hence, this study focuses on the fundamental mechanisms of nucle- ation, growth as well as aggregation and agglomeration during the nonaqueous synthesis and shows, on behalf of the model system zirconium dioxide, how the chemical reaction kinetics influence the size, morphology, and phase composition of the final nanoparticles. The presented results show that by varying the parameters temperature and initial precursor concentration, it is feasible to control the particle formation kinetics and, therefore, to customize the final nanoparticle properties.  Based on these results, a comprehensive simulation model using the population balance equation method was developed, which is able to describe the entire particle formation process for a broad range of process parameters. As a rational synthesis requires reactor systems that allow a precise control of the process parameters, a microfluidic system for the nonaqueous synthesis was developed where the synthesis is conducted in discrete droplet reactors. By exploiting the fast heat transfer rates in these systems, ho- mogeneous process conditions could be realized within the entire system, which yielded high-quality TiO2, CeO2, and ZnO nanoparticles.