Iridium provides global mobile telecommunications services using a constellation of 66 low earth orbit (LEO) satellites in a 86.4 BA inclined orbit.

Although 77 satellites were originally envisioned for the system and spawned the name based on the 77th element in the periodic table, the system has been scaled back.  Motorola's Satellite Communications Group designed and manufactured the Iridium satellites.

Unlike other mobile satellite systems, Iridium employs Inter-Satellite Links (ISL) to bounce signals from satellite to satellite using on-board signal processing. Each satellite is connected to its four neighboring satellites providing flexibility in where the ground network gateways are located.   These gateways connect the Iridium network to the public switched telephone network (PSTN).

The system offers a wide range of satellite based mobile telecommunications through mobile terminals manufactured by Motorola.   The service currently allows voice and paging capabilities. 

Iridium began commercial service in November 1998.  Due to shortfalls in revenue and subscription rates, Iridium filed for Chapter 11 Bankruptcy Protection on August 13, 1999.  

In December 2000 Dan Colussy, an aviation industry veteran, purchased the assets of Iridium LLC, including the satellite constellation and the terrestrial network for about US$25 million. Iridium Satellite LLC resumed service in March 2001, with cheaper prices. Among other customers, the U.S. Department of Defense has signed a multi-year contract for unlimited airtime for up to 20,000 government users.