This chapter addresses the motivations and mechanisms behind the following shifts. The structures and functions of Chinese passives underwent three typologically significant changes: (a) the passive morphemes in Old Chinese could not introduce any agent phrase in preverbal position, but those in Contemporary Chinese must introduce an agent noun to make the passive structure well formed; (b) the agent phrase could be introduced only in postverbal position in Old Chinese but is exclusively constrained to preverbal position in Contemporary Chinese; and (c) the passive morphemes are extremely diverse in Contemporary Chinese, including four markers in Mandarin Chinese and at least sixty-nine markers in the other dialects that have grammaticalized from different lexical sources but have quite uniform structures and functions, where the presence of an agent is generally obligatory.