This article reviews microwave biosensors that characterize dielectric properties of biological cells across the α, β and γ dispersion regimes. Sensors are applied to extract cellular parameters such as membrane capacitance, cytoplasmic conductivity, and intracellular hydration. Sensor types discussed include microstrip, coplanar waveguide (CPW), capacitive electrode, resonant structure and dielectrophoresis (DEP) sensors. Challenges addressed include detecting and confirming the presence of a cell, positioning the cell in the sensor region and maintaining positional stability. Finally, a number of considerations are examined including buffer composition, calibration, de-embedding and processing.