The last silver certificate was issued on March 25, 1964. It was on this date that Congress decided that silver certificates could no longer be exchanged for silver dollars.
Silver certificates were first introduced to American currency via an act of Congress on February 28, 1878. After silver certificates were discontinued in 1964, Congress decided on June 24, 1967 that those still in circulation could be exchanged for silver bullion for a time period of one year. The exchange of certificate for bullion ended on June 24, 1968. In modern times, any silver certificates still in circulation are legal and can be used as if they were a Federal Reserve Note.