July 1990 marked the 50th anniversary of one of the most critical and decisive struggles in the European theatre during World War II. Following the withdrawal of British forces at Dunkirk and the fall of France, the Battle of Britain pitted some 2,800 Luftwaffe aircraft against some 650 serviceable RAF fighter aircraft. For the next four months, Britain faced almost daily air attacks against airfields and military installations, ports, and civilian and industrial centres. The failure of the Luftwaffe to overwhelm and destroy the RAF undercut German efforts to mount an invasion of Britain, and by November the air war shifted to the "Blitz" phase, the attempt to destroy civilian morale through attacks on urban centres, which was to last for the rest of the war. "Dangerous Sky" attempts to bring together all the main sources published up till and including 1989 dealing with the battle. The guide provides information on how to conduct RAF research, and organizes materials ranging from official documents through memoirs and biographies to secondary histories under major categories. Within each category, materials are cited in alphabetical order and short descriptive comments are provided. Access to material is augmented by an author index. This research guide is intended to be useful to students, military buffs, and researchers concerned with the British side of this crucial phase of World War II.