A methodology that can be efficiently used to synthesize, isolate, and study out-of-equilibrium crystal structures employing controlled and diffusion-limited microfluidic environments is demonstrated. Unlike studies conducted with conventional mixing procedures in a flask, it is proven experimentally and with numerical simulations that microfluidic technologies can undoubtedly fine-tune reaction times and reagents concentration profiles; factors that enable out-of-equilibrium crystal forms to be obtained. ; The authors acknowledge the financial support from MINECO-Spain, under projects MAT2012-30994 and CTQ2011-16009-E, the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement no 615954 and from the Swiss National Science Foundation (SNF) through the project no 200021_160174. The authors thank the Microscopy Service of the UAB. M.R.-M. and C.C. thank the ICN2 for their research fellowship, I.I., N.D., and J.P.-L. thank the MINECO for RyC contracts. ICN2 acknowledges the support of the Spanish MINECO through the Severo Ochoa Centers of Excellence Program, under Grant SEV-2013-0295. ; Peer Reviewed