Generally speaking, there are four major American Jewish religious movements: Orthodox, Conservative, Reform, and Reconstructionist. In addition, there are a number of smaller movements that make up the wide variety of American Jewish religious movements.
The Orthodox movement, which arose out of nineteenth-century opposition to modernizing religious movements in Judaism, is based on the premise that Jewish law, in the form of the Torah, or five books of Moses, was given by God to the Jewish people via Moses on Mount Sinai and therefore cannot be changed. Therefore, practitioners of Orthodox Judaism are Torah observant, meaning that they faithfully observe all of the laws contained in the Torah that can still be performed. Of all the American Jewish religious movements, the Orthodox adheres most closely to traditional Jewish practices. There are wide variations, however, even within Orthodoxy itself.
The Conservative movement is a uniquely American Jewish religious movement that arose in the twentieth century as a more observant branch of the Reform movement. The Conservative movement understands Jewish law as the word of God, much like Orthodoxy, but also maintains that appropriate, thoughtfully considered changes in the law, based in knowledge and careful study, are necessary to maintain the relevance of Jewish practice in modern times.
So, for example, the Conservative movement has issued an opinion that allows for driving on the Sabbath, which is traditionally prohibited, only for the purpose of attending synagogue services, but its opinion in this matter relies on a particular interpretation of Jewish law made with an eye toward its modernization.
The Reform movement arose in nineteenth-century Germany as a response to Jewish political emancipation, assimilation, and modernization. The Reform movement posits that Jewish law is not divinely given, and therefore non-binding. Nonetheless, the Reform movement emphasizes Jewish ritual and tradition as a way of maintaining culture and community, as well as a religious sensibility that is consonant with the contemporary period. Within the scope of American Jewish religious movements, the Reform movement is also the most focused on external issues such as social justice.
The Reconstructionist movement is a hybrid practice that arose in twentieth-century America out of the Conservative movement. Founded by Mordecai Kaplan, Reconstructionism focuses on the individual's personal relationship with God and maintaining Jewish civilization and culture rather than strict adherence to traditional religious practices. Like Reform Judaism, Reconstructionism emphasizes general morality over Jewish law and theology. However, unlike the Reform movement, the Reconstructionist movement holds that people should try to incorporate Jewish law and practice into their lives as much as possible.
These four major movements do not by any means represent the entirety of American Jewish religious movements. However, taken together, they do represent the largest portion of American Jewish affiliation. Many smaller sub-groups exists within these major movements, like the many sects of ultra-Orthodox Jews, and many other smaller movements have also attracted many adherents, like Renewal Judaism and the independent minyan movement.Nonetheless, these four major American Jewish Religious movements, for the time being, hold the greatest sway in the American Jewish melting pot.