Microwave resonance cavities and associated methods and apparatus are described. In one example, a cavity (100) comprises a first and a second input port (102, 104) for inputting microwave radiation at a first and a second frequency respectively. The microwave radiation at the first frequency may be to excite a sample in the cavity whereas the microwave radiation at the second frequency may be to interrogate a sample in the cavity for analysis. The cavity has dimensions such that it resonates at both the first and the second frequency.