German scholar and Lutheran church historian noted for his investigations of Christian origins.

While a professor of classical philology and church history at the University of Jena (1905–24) and the University of Berlin (1924–42), Lietzmann began and directed the Handbuch zum Neuen Testament, 23 vol. (1906–31; “Handbook to the New Testament”). Impressed by his linguistic expertise in biblical interpretation, his colleagues, in 1920, chose him to edit the Zeitschrift für neutestamentliche Wissenschaft (“Journal of New Testament Scholarship”). He gained respect for his precision and depth of judgment, even when he overturned long-held opinions. He shed new light on the evolution of the eucharistic communion service with his Messe und Herrenmahl (1926; The Mass and the Lord's Supper), which detected a possible fusion of two distinct types of 1st- and 2nd-century prayer services. His extensive research on St. Peter and St. Paul provided insights into the development of the church's organization in 1st-century Rome. Geschichte der alten Kirche, 4 vol. (1932–44; A History of the Early Church), indicates the breadth of his scholarship.