- A conflict between the Federation and the Romulan Star Empire, known as the Tomed Incident takes place, the outcome of which led to the Treaty of Algeron. The treaty redefined the Romulan Neutral Zone, and as well, ended all Federation research into cloaking technology. Afterward, the Romulans go into a period of complete isolation. (TNG: "The Neutral Zone", "The Pegasus"; ENT: "These Are the Voyages...")
- The planet Meridian appears in the primary universe. It does not appear again until 2371. (DS9: "Meridian")
- Jillur Gueta is born on Bajor. (DS9: "Things Past")
- According to the script for "Sarek", Ki Mendrossen is fifty-five years old in 2366, placing his birth in or around this year.