<P> By the early 1960s , a more organized system was needed , and non-mandatory five - digit ZIP Codes were introduced nationwide on July 1 , 1963 . The USPOD issued its Publication 59 : Abbreviations for Use with ZIP Code on October 1 , 1963 , with the list of two - letter state abbreviations which are generally written with both letters capitalized . An earlier list in June had proposed capitalized abbreviations ranging from two to five letters . According to Publication 59 , the two - letter standard was `` based on a maximum 23 - position line , because this has been found to be the most universally acceptable line capacity basis for major addressing systems '' , which would be exceeded by a long city name combined with a multi-letter state abbreviation , such as `` Sacramento , Calif . '' along with the ZIP Code . The abbreviations have remained unchanged , with the exception of Nebraska , which was changed from NB to NE in 1969 at the request of the Canadian postal administration , to avoid confusion with the Canadian province of New Brunswick . </P>
<P> By the early 1960s , a more organized system was needed , and non-mandatory five - digit ZIP Codes were introduced nationwide on July 1 , 1963 . The USPOD issued its Publication 59 : Abbreviations for Use with ZIP Code on October 1 , 1963 , with the list of two - letter state abbreviations which are generally written with both letters capitalized . An earlier list in June had proposed capitalized abbreviations ranging from two to five letters . According to Publication 59 , the two - letter standard was `` based on a maximum 23 - position line , because this has been found to be the most universally acceptable line capacity basis for major addressing systems '' , which would be exceeded by a long city name combined with a multi-letter state abbreviation , such as `` Sacramento , Calif . '' along with the ZIP Code . The abbreviations have remained unchanged , with the exception of Nebraska , which was changed from NB to NE in 1969 at the request of the Canadian postal administration , to avoid confusion with the Canadian province of New Brunswick . </P>
when did the post office start using zip codes
when did the post office start using zip codes
July 1 , 1963
July 1 , 1963