[en] In order to obtain a quantitative description of the physical changes induced by radiation interacting with an important system in the condensed state, the case of electron interactions in water was studied. The task thus outlined is accomplished in two steps. First, numerical values of the inverse mean free paths (IMFP's) are obtained as functions of electron energy and energy loss. Second, a Monte Carlo transport code based on the IMFP's is developed to follow all primary and secondary electrons until their energies fall below a selected cutoff value. The spatial distributions of all atomic species produced are then tabulated. This approach is not phenomenological, but represents instead an attempt to formulate from first principles the actual events that occur. The program begun here will require some time to develop and to extend to biological systems. The present paper outlines this beginning and gives some preliminary results of the transport of pencil beams of 1keV and 10keV electrons through liquid water