This thesis assesses the usability of Online Grocery Systems (OGSs) in order to improve both customer satisfaction and uptake. This assessment was conducted in three phases using two different types of Usability Evaluation Methods (UEMs). Phase 1 was conducted using an expert review of 14 OGSs through heuristic evaluations and checklist/framework evaluations. Phase 2 was conducted using usability testing at one OGS that was deemed to be (based on the expert review in Phase 1) an OGS with good usability. The expert review was conducted by 54 participants with varying levels of online shopping experience. The results from the expert review (Phase 1) showed that the usability of the major Australian OGSs was comparable with those from other countries. The results from the usability testing (Phase 2) revealed usability issues with the OGS identified as having good usability, shown through the errors made by participants. The recording of errors in regards to the usability of systems has traditionally focused on safety-critical systems and business support systems. This study applies Zapf et al.’s ‘Taxonomy of Errors’ to a non-work related context: the OGS. The taxonomy was found to show that similar types of errors were made by all users of such systems. However, the number of errors that were recorded by different user groups varied. This finding was in contrast to previous studies, and supported the common perception that beginner users make a greater number of errors than more experienced users.