The major eruption of Mt. St. Helens on May 18, 1980, was recorded by infrared sensors aboard two U.S. Air Force satellites. The extent of the coverage and the completeness of the data base appear to be unique, providing information unavailable from other sources. The eruption was monitored essentially continuously, beginning at 15:32:57 UT, less than 1 min after the earthquake that appears to have been the triggering event. Dual satellite monitoring permits triangulation, so that both the lateral and vertical development of the ash emission can be determined with good temporal resolution. The data are being analyzed at the Space Sciences Laboratory of The Aerospace Corporation. Emphasis up to now has been placed on elucidating the sequence of events during the highly dynamic early eruptive phase, principally the period between initiation and the first GOES photograph at 15:45 UT. The resulting picture differs in many important respects from that inferred from photographs made by nearby observers, or from indirect evidence such as blast effects. The nature and timing of the principal events have been described in a report to the Society of Photo-optical Instrumentation Engineers (SPIE) Washington meeting and are summarized below.