For nearly 200 years the Qing dynasty practiced a form of adoption to secure orderly succession to the throne when the emperor was childless.
It was instituted by the Yong Zheng Emperor (reigned 1723-35), who decreed that an emperor could nominate his successor from among any of his sons, or if childless, appoint an heir from elsewhere in the imperial family, and the appointed heir was then generally adopted by the emperor, both to emphasize his choice and also so that he could perform the required funerary rites and later ancestor veneration.
The practice spread to other high-ranking members of the imperial family, where childless princes would adopt in order to have successors. See also, for example, the entries Roman Empire, Pomare Dynasty, Hawai'ian Royal Families, India (Princely States) and Eliezer. Some adopted Chinese emperors and nobles: