A new gas-phase electron diffraction apparatus is reported in this thesis. The machine complements the existing electron diffraction set-up at Edinburgh University. The new apparatus utilises an electron counting device consisting of a pair of stacked microchannel plates and a novel, position-sensitive anode counter rather than the photographic plate-rotating sector method more commonly used in electron diffraction studies. The work carried out with this detector is discussed together with results from a simulation program designed to evaluate the operational capabilities of the device under a range of experimental conditions. The molecular target source was provided by a Campargue-type molecular beam and the electron beam was produced by a telefocus electron gun. Both of these beams have been fully characterised and the results are presented in this work. A short review is given of the current developments in gas-phase electron diffraction. Finally, the structural refinements of two molecules studied using the photographic method are reported. These are 1,2-di-tert-butyldisilane and 1,2-dicarbapentaborane(7).