In this paper, a fully analytical model of the frequency selective indoor radio channel is presented. It is derived by combining fundamental principles of wave propagation with geometrical techniques and depends on a set of key parameters that characterize both the wave propagation within and the geometry of the surroundings for which the channel is to be modeled. The parameters are robust and easily available for system designers. The model is verified by simulations and measurements at 2.4, 5.25, and 60 GHz. It consists of a set of expressions which allow fast and precise link budget calculations for network planning and provide all quantities that are required for statistical generation of channel impulse responses. The presented analytical techniques are fairly general and may allow the development of similar channel models for more complicated channels, such as multiple inputs, multiple outputs or Ricean ones.