<P> As early as October 1831, the United States Post Office recognized common abbreviations for states and territories . However, they only accepted these abbreviations because of their popularity, preferring that patrons spell names out in full to avoid confusion . </P> <P> The traditional abbreviations for U.S. states and territories, widely used in mailing addresses prior to the introduction of two - letter U.S. postal abbreviations, are still commonly used for other purposes (such as legal citation), and are still recognized (though discouraged) by the Postal Service . </P> <P> Modern two - letter abbreviated codes for the states and territories originated in October 1963, with the issuance of Publication 59: Abbreviations for Use with ZIP Code, three months after the Post Office introduced ZIP codes in July 1963 . The purpose, rather than to standardize state abbreviations per se, was to make room in a line of no more than 23 characters for the city, the state, and the ZIP code . </P> <P> Since 1963, only one state abbreviation has changed . Originally Nebraska was "NB"; but, in November 1969, the Post Office changed it to "NE" to avoid confusion with New Brunswick in Canada . </P>

When did state abbreviations change to two letters