This book investigates a proposal by K. Stenring that the main chronology of the Old Testament is based on three different calendars. Complete agreement with given periods and dates in the Hebrew version of the Old Testament has been reached in this way. The solution is tested from mathematical and statistical viewpoints, its dates are compared with text information concerning seasons and Sabbaths and remarkable connections with ‘sacred’ periods and festival dates are found. The conclusion is that it must have been used in twelve books at a common redaction but then consciously concealed. The book further discusses ambitions of the system, specific chronology of the Divided Kingdom and relations to the Septuagint and to great historians of the time.