The size of the Court is not specified; the Constitution leaves it to Congress to set the number of justices.

When the cases in volume 307 were decided the Court comprised the following members: United States v. Miller, 307 U.S. 174 (1939), is a significant Supreme Court decision involving a Second Amendment to the United States Constitution challenge to the National Firearms Act of 1934 (NFA).

The case is often cited in the ongoing American gun politics debate, as both sides claim that it supports their position.

In Lane v. Wilson, 307 U.S. 268 (1939), the Supreme Court ruled that a 12-day, one-time voter registration window was discriminatory for black citizens and repugnant to the Fifteenth Amendment.

Perkins, Secretary of Labor v. Elg, 307 U.S. 325 (1939), is a decision by the Supreme Court that a child born in the United States to naturalized parents is a natural-born citizen, and that the child's U.S. citizenship is not lost if the child is taken to and raised in the country of the parents' origin, provided that upon attaining the age of majority, the young person elects to retain U.S. citizenship "and to return to the United States to assume its duties."