This paper analyses some general issues about human language technology evaluation, focusing on economic aspects. It first provides a scientific rationale for the need to organize evaluation in the form of campaigns, by relating this need to some basic characteristics of human language technologies, namely that they involve learning to process information in a way which reproduces human capabilities. It then reviews the benefits and constraints of these evaluation campaigns. Borrowing concepts from the field of economics, it also provides an analysis of the economic incentives to organize evaluation campaigns. It entails from this analysis that fitting evaluation campaigns to the needs of scientific research requires a strong implication in term of research policy and public funding.