Radioactive sealed sources are required for the treatment of many tumours and for industrial uses with, for example, Iodine-125, Iridium-192 and Palladium-103 as miniature sources. Miniaturization and high specific activity are the main parameters of modern sealed sources for most applications. This publication provides the methodology and technology of preparation of miniature sealed sources based on these radioisotopes for medical applications, as well as for industrial quality control. This publication provides practical information about the production of these miniature sealed sources and gives useful procedures for their encapsulation, welding techniques and quality control.