The "Establishment Clause" in the First Amendment of the U.S. Constitution prohibits the government from establishing an official religion. This clause ensures the separation of church and state, preventing the government from favoring or endorsing any religion over others. It was designed to protect religious freedom by ensuring that the government cannot impose religious practices on its citizens or support religious institutions with public funds. This foundational principle supports a diverse and pluralistic society, where individuals are free to practice any religion or none at all without government interference or preference.