Lightning discharges between a natural thundercloud and a point on ground can be artificially initiated using the so-called rocket-and-wire technique. This technique involves the launching of a small rocket extending a thin wire toward a charged cloud. In most respects the triggered lightning is a controllable analog of natural lightning. The results of triggered-lightning experiments have provided insight into lightning processes that would not have been possible from studies of natural lightning due to its random occurrence in space and time. Among such findings are detailed observations of lightning propagation and attachment to ground, discovery that all types of negative lightning leaders produce X-rays, identification of the M-component mode of charge transfer to ground, direct measurements of NOx production by an isolated lightning channel section, and many others. The first terrestrial gamma-ray flash (TGF) observed at ground level was associated with triggered lightning. Triggered-lightning experiments have contributed significantly to testing the validity of various lightning models and to providing ground-truth data for lightning locating systems. Triggered lightning is a very useful tool to study the interaction of lightning with various objects and systems.