This review article covers the work being carried out in the group of Jensen at MIT on microreactors, which are expected to have advantages, such as good heat and mass transfer, for scale up and production (Jensen K F, Chem Eng Science, 2001, 56, 293). Microreactors are natural platforms for combinatorial chemistry and for statistical experimentation, particularly in the field of catalyst synthesis and evaluation. The article concentrates on design of microreactors rather than the chemistry carried out. For more details of chemistry in microreactors see issue No. 6, volume 5 of Organic Process R & D, particularly the article by Taghavi-Moghadam et al on pp 652-658. For information on a commercial microreactor see www.cpc-net.com.