As the use of Information Technology (IT) increases, so does the need for accreditation of IT skills. Of the many Computer-Based Assessment (CBA) systems which claim to assess such skills, most are based on approaches such as multiple choice questions or atomic functions tests within controlled environments. In contrast, most professional qualifications in the UK, assessed by human examiners, focus on the output of authentic skills, that is, complete documents produced during realistic interactions with industry standard software. In order to automate the assessment of such examinations the expertise and knowledge of human examiners must be represented and the authentic nature of the assessment tasks retained. This paper describes a suite of Knowledge-based CBA systems for IT Skills, developed at the University of East Anglia, which have been deployed by a leading UK examination body to replace human markers for several of its flagship IT awards.