Spherically symmetric space-times have been studied in general relativity ever since the beginning when as the first exact solution of the Einstein equation the Schwarzschild space-time was given. Later on an elaborate local theory of spherically symmetric space-times was worked out with such fundamental results as Birkhoff's theorem and essential results concerning their global geometry have been achieved. Yet it seems that a general global theory is lacking even now. Some fundamental facts concerning the global geometry of spherically symmetric space-times are presented below. The concept of axis and of transverse submanifold are introduced and applied to study and classification.