With widespread interest in the generic “nano, attention has been focused on strategies to make small particles. While it is relatively easy to make inorganic nano-particles, for example CdS particles or Stober silica particles, it is much more challenging to make nanoparticles from low surface energy organic solids. The special advantages of nanoparticle drug formulations from highly hydrophobic compounds have driven research in this field. Strategies for forming nano particles vary from supercritical spraying, supercritical freezing, milling, solvent exchange precipitation, and imbibing into polymeric micelles. Our focus has been on “ultra fast” precipitations that involve two components: (1) rapid and tailored micromxing in an impinging jet to effect high supersaturations and nucleation rates, and (2) novel block copolymer stabilizers. The process depends critically on control of three time scales: particle nucleation and growth, block copolymer micellization, and polymer adsorption on the particle to produce steric stabilization. At the scale of “nano” several phenomena become significant in determining particle formation and stability. Curvature-induced solubility differences (Kelvin effect) drive diffusion-induced particle growth (Ostwald ripening). Crystallinity drives nanoparticle shape evolution. Curvature changes the free energy of compounds in nanoparticle cores (Laplace pressure) and limit drug loadings. And for polymer stabilized particles the soluble polymer brush layer controls the effective interfacial tension at the particle surface. This world of interesting phenomena at the nano scale and the technological importance of the field make it a rich area of investigation.