Most Americans believe in God, a majority pray and more than a third go to religious services every week. But these statistics tell little about spirituality in the United States, which has given birth to hundreds of religions and has arguably led the world in reinventing systems of belief. Now, because of changes due to immigration, population shifts, secularization, and increasingly liberal social and theological attitudes among young people, Americans are the midst of what may be its most profound religious transformation. This new HuffPost series, "Faith Shift," will examine that changing landscape.