What is the patent number for Tesla's basic radio patent?

Tesla’s basic radio patent is commonly identified as U.S. Patent 645,576.

The patent was titled “System of Transmission of Electrical Energy.” Tesla filed the application on September 2, 1897, and the United States Patent Office granted it on March 20, 1900. Its claims concerned high-frequency electrical oscillations, resonant circuits, elevated terminals, and the transmission of electrical energy through natural media.

Although the patent’s title emphasizes energy transmission rather than radio communication, it is frequently discussed as one of Tesla’s foundational wireless patents. Tesla’s related U.S. Patent 649,621, “Apparatus for Transmission of Electrical Energy,” is often mentioned alongside it, which can cause confusion when trivia questions ask for a single number.

The patent also became important in the later dispute over priority in radio. In 1943, the U.S. Supreme Court decision in Marconi Wireless Telegraph Co. v. United States considered earlier patents, including Tesla’s. That history does not make every radio invention Tesla’s alone, but it explains why 645,576 is the conventional answer to this question.