The invention provides a method for preparing a compound or a product having one or more characteristics that meet or exceed a user specification, the process comprising the step of selecting a first combination of chemical inputs, optionally together with physical inputs, and supplying those inputs to a reaction space, thereby to generate a first product; analysing one or more characteristics of the product generated; comparing the one or more characteristics against a user specification; using a genetic algorithm selecting a second combination of chemical inputs, optionally together with physical inputs, wherein the second combination differs from the first combination, and supplying those inputs to the reaction space, thereby to generate a second product; analysing one or more characteristics of the second product generated; comparing the one or more characteristics generated against the user specification; repeating the selecting and analysing steps for further individual combinations of chemical and/or physical inputs, to provide an array of products wherein the flow chemistry system operates continuously to provide the first, second and further products, thereby to identify one or more products meeting or exceeding the user specification.