The 4th International Symposium on Radiation Physics (ISRP-4) covered the following areas of radiation research: fundamental processes in radiation physics, radiation sources and detectors, uses of radiation in fundamental research, radiation in biomedicine and in environmental science, radiation in technology, and radiation in energy research. There were 24 invited papers and 110 posters. The meeting was attended by 173 participants — 90 from Brazil and 83 from 25 other countries. The proceedings will be published as a supplement of the journal Nuclear Instruments and Methods in Physics Research.