Leaks are small holes, interconnected pores, or capillaries crossing walls of a vacuum system. Probability of their occurrence is higher in detachable sealing areas and permanent welded or soldered joints. Accumulation methods are the cheapest techniques used in the identification of leaks because they do not require special detection facilities. These methods just need a gate valve between the vacuum system containing a leak, a pumping unit, capability to measure pressure on a timescale, and knowledge on the volume of the tested system. Some high-pressure methods for leak detection are very simple. These methods employ a proper gas to pressurize metal vacuum systems or smaller vacuum components. Blowing of a fine beam of testing gas on an inspected area is often employed in the leak detection. Mass spectrometric methods are the most elegant and sensitive techniques for leak detection. Radioactive methods of leak detection are highly sensitive techniques that are exploited at leak detection on small vacuum systems.