The ability to precisely analyse the composition of liquid mixtures by non-contact techniques in both static and flow situations is extremely desirable for a variety of industrial, analytical and QC procedures. Microwave resonators allow very accurate and sensitive characterisation of the dielectric properties of polar liquids due to the strong interaction of the latter with microwave electric fields. They offer tremendous potential for investigation of very small amounts of polar solvents in non-polar hosts. In this regard they are superior to other traditional compositional analysis methods such as liquid chromatography, gas chromatography and mass spectrometry in the speed of analysis, non destructive nature and scope for miniaturisation of the resonator to suit the system under test. Here, both lumped and distributed element microwave resonators have been used for analysing two-component mixtures flowing in microcapillary manifold systems. The experimental results are shown to be highly repeatable and extremely sensitive. It is expected that this book will greatly benefit researchers involved in compositional analysis experiments.