The Millennium Group is a fictional secret society featured in the crime thriller television series Millennium, and briefly on The X-Files. Having begun life as a Christian sect at the end of the 1st century AD, the Group grew into a far-reaching network which, as the 3rd millennium approached, presented itself as a private investigative firm liaising with law enforcement organizations. Despite being fraught with internal schisms, the Group tried on several occasions to artificially instigate the end of the world as the year 2000 approached.
The Millennium Group's role as an investigative organization was based on the real-life Academy Group, a society of retired law enforcement agents in the United States. The presentation of the Group varied as the series progressed, with its role changing from that of a benevolent investigative group to an antagonistic mystic sect. The Millennium Group has met with negative responses, with its vacillating depiction being a focus of criticism both from critics and from series star Lance Henriksen.