For decades, film was used as a powerful two-dimensional (2D) dosimetry tool for radiotherapy treatment verification and quality assurance. Unlike the old silver-halide based radiographic films, radiochromic films change its color upon irradiation without the need for chemical development. Radiation dose deposited within a sensitive layer of the radiochromic film initiates polymerization of the active component, the degree of which depends on the amount of energy deposited. Response of the film to radiation is commonly expressed in terms of optical density change, which can be easily measured by any photometric device. However, a number of factors may have an impact on the signal detected by the measuring device. This review summarizes technical aspects associated with the establishment of reference radiochromic film dosimetry and its subsequent use for either clinical or research applications.