Conservative Judaism, called Masorti outside North America, was built to occupy a position that its founders thought obvious and that both its neighbours regard as unstable: that Jewish law is genuinely binding and genuinely historical.
Its intellectual origin is the Positive-Historical school of Zacharias Frankel in nineteenth-century Germany, who walked out of a Reform rabbinical conference in 1845 over the proposal to abandon Hebrew as the language of prayer. Frankel held that Judaism is the possession of the whole people and develops through their practice over time, so that change is legitimate when it grows from the tradition and illegitimate when it is imposed on it by reformers with a programme.
In America the movement took institutional shape around the Jewish Theological Seminary, refounded in 1902 under Solomon Schechter, and it grew enormously in the mid-twentieth century among immigrant families who wanted a Judaism that was recognisably traditional and comfortably American. For a period after the Second World War it was the largest Jewish denomination in the United States.
The characteristic move is to accept the findings of critical scholarship about the composition and history of the biblical text while continuing to treat the law derived from it as commanded. Orthodoxy holds that the first position destroys the ground of the second. Reform holds that the second is an unnecessary burden once the first is granted. Conservative Judaism holds that the covenant obliges the people whether or not the text descended in one piece at Sinai, and that the argument from history is precisely what licenses careful development.
Whether that position is coherent is the single most argued question about the movement, and it is argued inside it as much as outside.