Abstract: Perhaps the major difficulty in evolving circuit designs is the fact that the switches used to make and break connections between the core functional devices in the circuit have a high resistance and a highly nonlinear current-to-voltage relationship. Every single switch adds complexity to simulation, often to the point of making the resulting circuit unsimulatable. Circuits which have been evolved cannot reliably be understood in terms of the core devices, and the circuit cannot be mapped to a hardwired structure. A promising solution is to build physical switches using a MEMS (Micro-Electomechanical Systems) process. Switches formed from mercury microdrops make excellent reprogrammable contacts, and can be fabricated in a planar process on top of electronic circuits prefabricated in a standard CMOS technology. The technology is also expected to apply to programmable analog arrays, and, if process refinements can maintain yield while decreasing the size of the droplets, may even be a competitive technology for FPGA devices.