This chapter explains some of the issues involved in using various indicators of output in productivity analysis. One of the main difficulties in determining levels of productivity in the construction industry has been determining levels of output. The way construction industry productivity has been analyzed, and the way in which outputs and inputs have been compared to each other, has been influenced by the manner in which productivity analysis more generally has developed. In the construction industry, there are a number of problems that have arisen in the determination of output measures which are fairly unique to the industry. In the construction industry, physical measures are difficult to use because of the varied nature and complexity of buildings, and the traditional financial measure of value added is also problematic as the industry increasingly moves to off-site fabrication. Most studies estimate the construction industry as possessing the greatest shadow economy compared to normal production.