Halo has been in development since around the end of Myth's development, during the winter of 1997. It proceeded through the development of Myth II, briefly interrupted by the final development phase of that game.

At the time of this update in October of 2001, Halo has been in development of some sort or another for nearly four years.

When development began, Halo was slated for a simultaneous release for the Windows and Macintosh platforms sometime in 2000.

The game was first announced at the Macworld Expo in New York, on July 21st, 1999. Apple CEO Steve Jobs gave the floor to Jason Jones, who demonstrated build of Halo running on Macintosh hardware in real time using OpenGL. The various quicktime versions of this event are collectively referred to as
the MWNY demo. At the time, Jobs stated that Halo would be released early next year.

However, in the summer of 2000 Bungie Software Products was purchased by Microsoft in order to become the premier in-house game developer for their upcoming gaming console, the Xbox, and development was shifted to that platform.

After a few nervous weeks, Bungie confirmed that despite this situation, a version of Halo would later be released for the Windows and Macintosh platforms, but a release date has not been given.