For the characterization of components, systems and signals in the range of microwave and radio-frequencies (RF) specific equipment and dedicated measurement instruments are used. In this article the fundamentals of RF signal processing and measurement techniques are discussed. It gives complementary background information for the introduction to RF Measurement Techniques and the Practical RF Course, which are part of the Advanced Accelerator Physics training program of the CERN Accelerator School (CAS) and have also been presented at the CAS 2018 Special Topic Course in Beam Instrumentation.