After two very expensive National Jewish Population Surveys (1990 and 2000) and more than 55 local Jewish community studies, the number of American Jews is still unknown, with estimates varying from 5.2 million to 6.4 million. Even the question of whether the number of American Jews is increasing, decreasing, or remaining the same is a controversial issue. The American Jewish Year Book estimates have shown a steady rise over the past decade, increasing from about 5.9 million to 6.4 million, while the NJPS estimates indicate a relatively static population size. This presentation explores some of the methodological drawbacks that contribute to the difficulty in making estimates.