This thesis investigates the application of multimodal metaphors in electronic Customer Loyalty Management Systems (e-CLMS) in terms of efficiency, effectiveness, user satisfaction, and understandability of the customisation tasks and information communicated. The potential of users developing loyalty as a result of better usability and user satisfaction is also accessed via questionnaires. The first experiment investigated issues of usability and the users' views of an e-commerce platform developed for these experiments using three conditions with three independent groups. A visual group (VICLMS, n=25) that was communicated information within the platform using text with graphics, a multimodal group (MICLMS, n=25) that usedrecorded speech, earcons and auditory icons and an expressive avatars group(AICLMS, n=25) that was predominantly communicated information using avatars. The second experiment evaluated three avatar-based multimodal conditions using a dependent group (n=50). This experiment evaluated user satisfaction, perceived convenience, enjoyment, ease of use and customisation, and successful completion of user tasks. The conditions were avatars with earcons (AEICLMS), avatars with auditory icons (AAICLMS) and avatars with both earcons and auditory icons (AICLMS).The use of expressive avatars in the e-CLMS interface contributed to the positive predisposition of usersto develop loyalty. Multimodal metaphors contributed more significantly to complex customisation tasks. A set of empirically derived guidelines and a validation approach is suggested for designing multimodal E-CLMS interfaces.