The Great Migration Begins includes more than one thousand sketches, each dedicated to a single immigrant or an immigrant family, arriving in New England between 1620 and 1633. Each sketch contains information on the immigrant's migration dates and patterns, on various biographical matters (including occupation, church membership, education, offices, and land holding), and on genealogical details (birth, death, marriages, children, and other associations by blood or marriage), along with detailed comments and discussion, and bibliographic information on the family. The latest update to this database (30 July, 2002) includes an additional 10 sketches.

The Great Migration Study Project (of which The Great Migration Begins is the first phase) aims to investigate all immigrants to New England from 1620 through 1640, with the goal of summarizing all research carried out by previous workers, and providing a solid platform which will allow future researchers quickly to assess the status of research on a given family, without having to repeat work already done, or waste large amounts of time searching the genealogical literature. To this end, the sketches on individual immigrants or immigrant families first review the existing secondary literature, looking especially for conflicting or missing data. Then the primary sources are examined in order to confirm what has already been written about the family, or to fill in the gaps, or to resolve conflicting interpretations and correct errors. In many instances, of course, gaps and discrepancies will remain, and the sketch will then describe the problem, and perhaps suggest a future course of research. In the end, the Great Migration sketches should permit future researchers to use their time more efficiently, and should also serve as a springboard for new discoveries.