Digital radiography is progressively replacing conventional (film-based) radiographic techniques promising consistently high levels of image quality, more effective use of radiation and more efficient work practices. At the same time its introduction poses new challenges to those physical scientists who design radiological imaging systems and those who provide scientific/technical support to a clinical radiology service Scientific aspects of those digital X-ray imaging systems which are proving most successful are described. Physical measurement techniques developed to evaluate the imaging performance and radiation dose efficiency of clinical digital radiography systems are outlined. Directions in which digital X-ray imaging technology may evolve in the 1990s are discussed.