This testimony summarizes in four propositions results from a review of recent estimates of the net federal, state, or local costs of immigration and is designed to explore why these cost estimates vary so widely and how to develop more credible cost estimates. First, the testimony proposes that various studies of the cost of immigration agree only that currently illegal immigrants are net consumers of public services. Second, that there is no agreement and no reliable estimate of the size of that net public cost for three major reasons: because studies differ in their estimates of the size and incomes of the immigrant population, because of different ranges of public services and public revenues included in the estimates, and because there is a lack of reliable information on such basic parameters as number of immigrants, their incomes, and their tax rates. Third, that the true net cost of immigrants must come from a consistent accounting framework and collection of additional data. Fourth, the testimony concludes that, in a departure from the past, these cost questions have been considered in connection with determining how many immigrants should be allowed to enter the country annually. (JB)