This talk will explore some of the methodological issues involved in a cost–benefit analysis framework for large scale capital-intensive research infrastructures. We propose a conceptual model based on the estimation of quantities and shadow prices of cost aggregates, and of six main categories of economic benefits: technological spillovers, human capital formation, knowledge outputs, cultural effects, services to third parties including consumers, and a public good, the pure value of discovery. We justify the reasons why these benefits of research infrastructures should be often expected to be the core ones in ex-ante project evaluation. Other benefits may be considered as well, but often by qualitative methods only. Empirical approaches are suggested for further applied research.