Abstract: A method and apparatus for determining the permittivity of a sample is disclosed. The method includes applying an AC electrical signal in the microwave frequency range via a coaxial probe having an end position near the sample and measuring the reflection coefficient of the sample. The complex permittivity of the sample is determined from an admittance parameter of the sample/probe combination and a system constant. The system constant is determined by measuring the reflection coefficients of four standards having known complex permittivity. The admittance parameter of the sample/probe combination is determined from the admittance parameters of two standards/probe combinations and the measured reflection coefficients of the sample and the four standards. The admittance parameters of the two standard/probe combinations are determined from the known complex permittivities of the two standards and the system constant.