Abstract: Microscale, monolithic heat or heat and mass transfer systems: a plurality of shims (102, 104) assembled between two outer plates (110, 111) that, when combined, form discrete but integrated heat and mass transfer system components that make up a microscale, monolithic absorption cooling and/or heating system, or other heat or heat and mass transfer system. The shims generally include a plurality of microchannels (702), voids, fluid passages, and other features for transferring fluids between defined components throughout the system, and into and out of the system to and from heating and cooling sources and sinks as needed. Generally, two distinct shim types are used and combined together as a plurality of shim pairs to enable thermal contact between the fluids flowing within the microchannels in each shim pair, each shim in each shim pair comprising slightly different microchannel and fluid passage arrangements as compared to each other.