Pipelines are the least expensive and most efficient way to move liquids and gases over land, but there is a high potential risk of danger in case of leak. This paper therefore describes pipeline leak detection technologies and emergency shutdown protocols ensuring reliable and safe pipeline operations. It starts by listing requirements and performance criteria and highlighting regulation issues concerning leak detection. Relevant regulations related to leak detection from U.S.A. and Germany are listed. The next part is a short summary of external-based leak detection systems according to the definition found in [API RP 1130]. These systems provide very good performance but investment and operational costs are usually very high, and in many cases it is impossible to retrofit existing pipelines with this type of leak detection system (LDS). Therefore, external systems will only be used in critical applications, for example when pipelines cross nature reserves or high consequence areas. Consequently, the main focus of this paper is on internal leak detection systems. These systems usually run continuously. Sensitivity is somewhat lower than for external systems, but so are investment and operational costs. For this reason, internal systems are very common and are required by law for some countries. Internal LDS are classified into two categories: Balancing methods using the principle of mass conservation, and non-balancing methods evaluating pressure and/or flow signals according to assumptions about signal characteristics. Applying model-based techniques for balancing methods leads to RTTM-based methods (RTTM = real time transient model) resulting in a significant shorter leak detection time. After a LDS leak alarm declaration, appropriate actions are required to limit the consequences of a leak, to protect people and environment, to take appropriate emergency actions etc. The last part of the paper therefore is devoted to emergency shut-down protocols initiated manually and/or automatically after a leak alarm.