The experimental study of magnetospheric processes consists of several disci­ plines or methods, developing in two general directions. The first, internal trend covers the progress in experimental techniques and methods and re­ search specific to this discipline. The other trend combines with other methods in a mutual attempt at understanding the boiling whirlpool of the disturbed magnetosphere. Investigations of auroral X-rays began after Van Allen's (1957) discovery of hard radiation in the upper atmosphere of the auroral zone, and are based on high latitude balloon observations. Scientific apparatus, payload equip­ ment, and particular questions of scientific ballooning are discussed in Chap­ ter 1. Chapter 2 concludes the internal trend of the subject by describing the problems of X-ray generation at the boundary of the atmosphere and propa­ gation downward to balloon altitudes. Auroral X-rays are closely related to most of the processes of the disturbed magnetosphere through energetic auroral electrons; precipitating into the at­ mosphere, the latter create bremsstrahlung photons able to penetrate to an at­ mospheric depth of 10- 20 g cm - 2. In quiet periods auroral electron flux ex­ ists only in embryo, as a hot plasma layer at the inner edge of the plasma sheet: in general it is a transient phenomenon caused by magnetospheric distur­ bances and carrying valuable information of the magnetospheric dynamics.