Since the ionosphere is produced by the quiet Sun and disturbed by the active Sun, short-term ionospheric forecasting is discussed in three stages:(1) forecasting the solar activity;(2) the relations between the solar activity and geophysical disturbances, particularly magnetic storms, daylight fadeouts and polar cap absorption;(3) the effects of these geophysical disturbances on the ionosphere and on ionospheric radio communications.A short history of the subject is given, the international arrangements for collecting and rapidly exchanging the required solar and geophysical data are outlined, and short-term forecasting services at present operating are described briefly.