Chapter 4 takes a diachronic perspective to the grammatical structure of academic writing, documenting the increasing use of phrasal complexity features in academic writing, and science writing in particular. The chapter presents a series of case studies comparing science prose to fiction and news reportage from the 18th century to present day. The analyses show that the stereotypes about grammatical complexity in academic writing (with a dense use of dependent clauses) provide an accurate portrayal of science writing in earlier centuries, suggesting the source of characterizations of academic writing as ‘elaborated’ and ‘explicit’. This chapter further demonstrates that the phrasal style of present-day academic research writing is a recent innovation, and not attested in any register in the 18th and early 19th centuries. We argue that it thus represents one of the most important recent grammatical changes in English. This chapter further shows that extensive register diversification has taken place over the last three centuries. We explore how these changes came about, and what societal forces may have influenced the course of change, including the use of colloquial forms in writing (’popularization’), and the need to efficiently convey a great deal of information (‘economy’) resulting in a discourse style that relies extensively on phrasal complexity features.