Research outputs are growing in number and frequency, assisted by a greater number of publication mediums and platforms via which material can be disseminated. At the same time, the requirement to find acceptable, timely, objective measurements of research "quality" has become more important. Historically, citations have been used as an independent indication of the significance of scholarly material. However, citations are very slow to accrue since they can only be made by subsequently published material. This enforces a delay of a number of years before the citation impact of a publication can be accurately judged. By contrast, each new citation establishes a large number of co-citation relationships between that publication and older material whose citation impact is already well established. By taking advantage of this co-citation property, this thesis investigates the possibility of developing a metric that can provide an earlier indicator of a publication's citation impact. This thesis proposes a new family of cocitation based impact measures, describes a system to evaluate their effectiveness against a large citation database, and justifies the results of this evaluation against an analysis of a diverse range of research metrics