Many methodologies exist for dividing a population into those who are classified as eligible for social transfers and those who are ineligible. Popular targeting mechanisms include means tests, proxy means tests, categorical, geographic, community-based and self-selection. This paper reviews empirical evidence from a range of social protection programmes on the accuracy of these mechanisms, in terms of minimising four targeting errors: inclusion and exclusion, by eligibility and by poverty. This paper also reviews available evidence on the various costs associated with targeting, not only administrative but also private, social, psycho-social, incentive-based and political costs. Comparisons are difficult, but all mechanisms generate targeting errors and costs. Given the inevitability of trade-offs, there is no ‘best’ mechanism for targeting social transfers. The key determinant of relative accuracy and cost-effectiveness in each case is how well the targeting mechanism is designed and implemented.