In this work, a detailed experimental analysis of the nanoparticle formation dynamics and the formation mechanism in a reverse microemulsion system is given. The precipitation of barium sulfate nanoparticles inside microemulsion droplets is investigated at the molecular scale with respect to the evolution of the particle size distribution and the particle morphology by an extensive transmission electron microscope (TEM) analysis. Different mixing procedures (feeding strategies) of two reactants, barium chloride and potassium sulfate, are evaluated concerning their ability for a tailored particle design under consideration of the complete particle size distribution (modality and polydispersity). It is shown that improved knowledge about the particle formation mechanisms, the dynamics, and the influence of the colloidal microemulsion structure could be used for a tailored design of particles,for example, controlled synthesis of nanoparticles with a bimodal particle size distribution by the application of a sophisticated feeding strategy.