According to the present invention there is provided a method of carrying out a chemical reaction between at least two fluids, the method comprising providing respective flow paths for the at least two fluids, said flow paths communicating with each other in a region in which the at least two fluids may contact each other, and flowing the at least two fluids along said flow paths such that in said region the at least two fluids contact each other and a chemical reaction occurs between them, said region having a width perpendicular to the direction of flow in the range 10-10,000 micrometers. It has been found that using a so-called “microreactor”, that is a reactor having dimensions perpendicular to the flow direction of less than 10,000 micrometers, according to the present method, improved control over a fluid chemical reaction can be achieved, which can result in significant improvements in reaction product yield and/or purity, as well as other benefits. The present method has been found to be particularly beneficial for fluorination reactions.