1973 is a year in the 20th century.
- October: John Lee Roche sells an Electrovac Princess to William Mulder for his wife Teena. (TXF: "Paper Hearts")
- October 13: A group of government agents make contact with a group of Greys. Afterward they form the Syndicate. The Syndicate soon afterwards begin experiments on human/alien hybrids. Bill Mulder highly objects to this act. (TXF: "One Son") Although the aliens agree to wait fifty years until they colonize the Earth, the Syndicate is forced to keep the colonization plans secret. (TXF: "The Truth")
- November 27: Cassandra Spender, the Cigarette Smoking Man(?), is among the group of Syndicate loved ones abducted as collateral, but is later returned. She becomes a test subject for the Syndicate's hybridization efforts. (TXF: "Two Fathers")
- November 27: Samantha Mulder is abducted from her home in Chilmark, Massachusetts. Her brother, Fox, is the only witness to the abduction. (TXF: "Little Green Men") She is also later returned, and begins to live with the Cigarette Smoking Man and Jeffrey Spender, while undergoing hybrid tests. (TXF: "Closure")
- Ish is present at Wounded Knee and fights various FBI officials. (TXF: "Shapes")
- Bill Mulder gets his picture taken in New York City alongside other Syndicate officials including Deep Throat, Victor Klemper, the Well-Manicured Man, and the Cigarette Smoking Man.
- The US Department of Defense officially declares that there are no more POWs in Vietnam after the Vietnam War. (TXF: "Unrequited")
- Alfred Fellig sends a renewal form to the New York City Police Department in order to keep his position as a crime scene photographer. (TXF: "Tithonus")
- Bill Mulder takes a picture with the Cigarette Smoking Man. (TXF: "Two Fathers")