This thesis investigates the topic of near-end crosstalk, applied to optoelectronic integrated circuits (OEICs). It concentrates on long-wavelength indium phosphide based devices, developed for telecommunications applications. The first example OEICs are emerging which combine the functionality of transmitter, and also receiver, on the same monolithic substrate. The inclusion of elements which operate with such greatly differing signal levels brings with it issues of crosstalk isolation which it has not been necessary to examine in such detail before. The thesis examines a representative set of experimental OEIC transceiver chips of varying complexity, each including an integrated laser, photo-detectors and waveguide structures on a single chip. These are incorporated into module packaging, and used as a vehicle to demonstrate the crosstalk mechanisms which are likely to be significant in future OEIC realisations. Modelling is presented which predicts the behaviour of particular crosstalk contributions in such modules, and this is used to compare with detailed measurements of real OEIC devices. Design rules are discussed for the production of OEICs with enhanced crosstalk suppression and OEIC designs for other applications are examined for crosstalk susceptibility.