In this review paper, scattering of intermediate to high energy electr
ons on well-known as well as exotic molecular targets is considered. T
he 'additivity rule' and its modifications for calculating various tot
al cross sections are discussed against the background of an extensive
experimental data. The theory succeeds at high impact energies (E-i >
100 eV). Tentative upper and lower limits of e-molecule ionization cr
oss sections are identified. Fitting formulas to represent total cross
sections as functions of energy are also given.