Radar is a technology that can be used to detect distant objects not visible to the human eye. A predecessor of radar, called the telemobiloscope, was first used to detect ships in the fog in 1904 off the German coast. Many scientists have worked on the development and refinement of radar (Hertz with electromagnetic waves; Popov with determining the distance of lightening strikes; Hulsmeyer with detection of metallic objects). During World War II, radar was further developed by several nations (including the U.K. and U.S.) to detect planes and ships that were entering into a nation's coastal zones. This early warning system allowed time for military forces to prepare to defend themselves (position troops with antiaircraft guns and artillery and to get aircraft squadrons into the air) and for civilians to seek shelter (air-raid shelters and basements). A U.S. Navy radar technician supposedly identified incoming Japanese planes in the attack on Pearl Harbor in 1941, but the reporting officer did not trust the findings with the new technology, since it was so unreliable at that time. Consequently, no warnings were issued prior to the attack, and many U.S. naval ships and aircraft were destroyed and countless lives were lost. This information resource will explain the concept of radar technology. It will review how a radar system works and some applications where it is used every day. Activities for learning more about radar will be presented.