Evaluating the impact on market performance of investments in agricultural market information systems (MIS) face several methodological challenges. These fall into two broad categories: (a) defining the dimensions of market performance to measure (which is a function of whom the MIS is designed to serve) and identifying reliable indicators of those performance dimensions, and (b) identifying the causal effects of the MIS. The determination of causal effects in turn requires establishing a credible baseline, measuring “treatment effects” (i.e., the effects on economic behavior of receiving improved information from an MIS), dealing with problems of endogenous placement of treatment, and interpreting the validity of stakeholders’ statements and governments’ revealed preferences regarding the utility of MIS. Many of these challenges arise because improved market information can affect the welfare of market actors through improved market polices and increased competition even if those actors do not have direct access to that information. The paper discusses these challenges and identifies approaches that may be useful in developing a “convergence of evidence” concerning whether investment in a given MIS is socially worthwhile.