Creating genetic devices for use in micro-organisms or other biological systems is described. In an embodiment a computer system receives at a program editor, input specifying a plurality of part designs, at least some of which comprise part properties expressed as logical variables; and the input also specifies constraints on the logical variables. For example, the input is a computer program which specifies constraints on the logical variables which, for example, relate to properties of the DNA sequences such as reactions and biological behaviors. In an example, a compiler resolves the constraints using a database of genetic parts in order to generate candidate parts for the proposed genetic device. In examples the sequences of genetic parts are translated into reactions and simulated using an automated simulator and/or implemented in a living cell or other biological system. In embodiments the compiler also uses a database of reactions.