The most cherished and argued about Amendment to the Constitution.
Amendment I: Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances
Religion:
The Constitution does not say anything about 'separation of church & state'. That phrase is taken from a writing of Jefferson in which he said that he believed that the 1st Amendment created "a wall of separation between Church and State". What the Constitution does say, and what the federal court system has been tasked with interpreting regarding religion is:
Congress shall make no law respecting an establishment of religion (establishment clause) nor prohibiting the free exercise thereof (free exercise clause)
Establishment clause:
Lynch v Donnelly
McCreary County v ACLU
Van Orden v Perry
Everson v Board of Education
Engel v Vitale
Lemon V Kurtzman
Wallace v Jaffree
Free exercise clause:
Reynolds v US
Minersville School District v Gobitis
WV State Board of Ed v Barnette
Wisconsin v Yoder
Speech & Press:
Congress cannot make a law abridging the freedom of speech or of the press. But, again, that is not absolute. There are limits. The Court has traditionally protected individuals from defamation by way of slander (spoken) and libel (print). The Court has also traditionally protected the government in its attempts to prevent treason and sedition.
Speech:
Schenck v US
Whitney v California
Brandenburg v Ohio
Press:
New York Times Co v Sullivan
Reno v ACLU
Near v Minnesota
New York Times Co v US
Symbolic Speech:
Tinker v Des Moines Independent Community School District
Texas v Johnson
Assembly & Petition:
Congress cannot abridge the right of the people peaceably to assemble. The people also have the right to petition their government for a redress of grievances. (Hence, all of those lobbyists people love to hate are legit)
DeJonge v Oregon
Edwards v South Carolina
NAACP v Alabama