A droplet-based microfluidic method for the preparation of anisotropic gold nanocrystal dispersions is presented. Gold nanoparticle seeds and growth reagents are dispensed into monodisperse picoliter droplets within a microchannel. Confinement within small droplets prevents contact between the growing nanocrystals and the microchannel walls. The critical factors in translating macroscale flask-based methods to a flow-based microfluidic method are highlighted and approaches are demonstrated to flexibly fine tune nanoparticle shapes into three broad classes: spheres/spheroids, rods, and extended sharp-edged structures, thus varying the optical resonances in the visible-near-infrared (NIR) spectral range. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.