After its successful encounter with comet P/Halley and a four-year hibernation period ESA's Giotto spacecraft has been reactivated in February 1990 and performed the first-ever Earth gravity-assisted maneuver on July 2, 1990 to be retargeted for comet P/Grigg-Skjellerup. This swing-by is of unique scientific interest due to Giotto's hyperbolic, high-inclination orbit. Here, we shall report on scientific results of the Giotto magnetic field experiment. Due to the high fly-by velocity and the relative quietness of the magnetosphere during the swing-by period these measurements present a snapshot view of the Earth magnetosphere with clearly identified inbound and outbound bow shock and magnetopause crossings. The outbound crossings are of particular interest as surface waves at the polar magnetopause at a distance of 28 RE as well as a strong quasi-perpendicular bow shock at a distance of about 64 RE are observed. ¿ American Geophysical Union 1991