Is it required by law?
The formal basis for the State of the Union address is from the U.S. Constitution:
• The president “shall from time to time give to the Congress information of the State of the Union, and recommend to their Consideration such measures as he shall judge necessary and expedient.” Article II, Section 3, Clause 1.
What's in a name?
The constitutionally mandated presidential message has gone through a few name changes:
• It was known as the Annual Message from 1790 to 1946.
• It began to be informally called the "State of the Union" message/address from 1942 to 1946.
• Since 1947, it has officially been known as the State of the Union address.
• There have been 96 total in-person addresses from 1790 to 2018. In 1945, President Franklin Roosevelt's address was read to a joint session of the House and Senate. Since the president did not deliver the address, it does not count as an in-person address.
• President Thomas Jefferson began the practice of sending separate, written Annual Messages to the House and Senate, instead of an in-person address, in 1801. This remained the practice of presidents until Woodrow Wilson revived in-person delivery before a joint session of Congress in 1913.
• Some Presidents have sent a written Annual Message or State of the Union address rather than delivering it in person. These include Presidents Woodrow Wilson (1919, 1920), Calvin Coolidge (1924-1928), Herbert Hoover (1929-1932), Franklin Roosevelt (1944, 1945), Harry Truman (1946, 1953), Dwight Eisenhower (1956, 1961), Richard Nixon (1973), Jimmy Carter (1981).
The other party's response
The practice began in 1966 when the television networks provided the Republican party with a half-hour slot. Sen. Everett Dirksen (R-Ill.) and Rep. Gerald R. Ford (R-Mich.) delivered the first opposition response. By 1976, the television networks were providing a slot for the opposition party almost immediately after the State of the Union address.
Where and when?
A House concurrent resolution sets aside the day and time for a joint session “for receiving such communication as the president of the United States shall be pleased to make to them” and is passed by both the House and Senate.
The ratification of the 20th Amendment on Jan. 23, 1933, changed the opening of Congress from early March to early January, affecting the delivery of the Annual Message. Until 1934, the Annual Message was delivered every December. Since then it is delivered every January or February.
To the masses
• First radio broadcast of message: President Calvin Coolidge, 1923.
• First television broadcast of message: President Harry Truman, 1947.
• First televised evening delivery of message: President Lyndon Johnson, 1965.
• First live webcast on internet: President George W. Bush, 2002.
• First high definition television broadcast of message, President George W. Bush, 2004.
• The longest: President James Earl (Jimmy) Carter 33,667 words in 1981 (written). President William J. (Bill) Clinton 9,190 words in 1995 (spoken).
• The shortest: President George Washington, 1790, 1,089 words.
Source: The U.S. House of Representatives