How many Jews are there in Canada? The answer depends on how being Jewish is defined, and by whom. Canada's national statistical agency collects data on religion and on ethnic origin and thus offers the possibility of establishing an official number. While most Canadian Jews declare both their religion and ethnicity as Jewish, an important number define themselves as either one or the other. Underlying such declarations is an ongoing debate about what it means to be ethnically Jewish. What does the use of ethnicity as a basis for determining community membership imply in defining Canadian Jewish identity? Using census and survey data, "Canadian Jews in the 21st century: Identity and Demography" explores the meaning of ethnicity for Canadian Jewry.