Some areas of appraisal in construction claims have commanded extensive attention, whilst others have failed to do so. Plant claims unquestionably fall into the latter category. Whether that is because the subject-matter is regarded—at one extreme—as too complex, or—at the other—as too simple to warrant serious study,1 is unclear. Thus, typically, the evaluation of the plant component of any construction prolongation claim is said (depending on the way in which the particular item of plant is deployed to the relevant project) to involve a simple choice between ownership costs and hire rates over the relevant period. This belies the importance of the subject (given, for example, that the cost of plant is at the present day likely to constitute a very significant proportion of a construction contractor’s total project costs) and its true challenges. The issues to be addressed can often involve complexities, both conceptual and factual, at all stages in the evaluation process—such as the appropriate approach to valuation and an understanding and sensible application of the array of different costs likely to be involved.