Radiometry is an essential part of the optical design of virtually every optical instrument, and key to many applications. It is also used to measure the radiation of various objects. This tutorial examines both the techniques of calculating radiative transfer and the measurement of fluxes and radiometric properties of various sorts. Contents - Introduction - Radiometric Quantities, the Language - Radiative Transfer - Transmission, Reflection, Emission, and Absorption - Radiance - Sources - Detectors - Review of Optics - Normalization - Calibration Standards - Measurement Techniques - Measurement of Fluxes - Measurement of Material Properties - Radiometric Temperatures - Polarization Effects - Some Geometric Configuration Factors