We all have one, we know it by heart, and we share it with our neighbors. But chances are you haven't thought that much about this ubiquitous part of American life — the ZIP code.

We all know about the middle-class and suburban boom in the U.S. following World War II, but as the Postal Service's Maureen Marion explains, that wasn’t the only thing booming.

"Not only boomtime for growth but boomtimes for volume of mail that was coming forward," Marion said.

Advertising, business mail, postcards, you name it. From 10 billion in 1933 to 20 billion in 1944 to 30 billion in 1956. In promo video from the era, the post office says it was in danger of being "swamped, overwhelmed, drowned in a sea of mail."

A fix was needed. In the 1940s, some large metro areas, like Boston, started to divide their mail delivery into zones, each represented by a two-digit number. Mike Powers, who runs the Greater Boston postal district, explains.

"It was called the Postal District code, so it’d be Boston, 21, Massachusetts and that would highlight the area," Powers said.

But the system wasn’t universal, and it quickly proved inadequate. So the postal service scaled it up, launching the Zone Improvement Plan — an elegant, ultimately simple system known by the serendipitous acronym, ZIP.

The first of five digits indicates one of nine regions of the country. The zero represents Massachusetts, Vermont, Maine and other New England states. A one indicates mid-Atlantic states like Delaware, Pennsylvania and others. all the way over to nine which is California.

The next two numbers indicate which sectional center the mail goes to. Here in Massachusetts it works in increasing order, from west to east. The Springfield area is 010, the Berkshires 011. By the time you get to the Cape and Islands it's 025 and 026.

The last two numbers are essentially your town or local post office.

ZIP has proved incredibly resilient. In 1983, the postal service got even more specific, with ZIP+4. But thanks to technology, you don’t need even need to know those last four digits.

"Technology today is remarkable," Powers said. "Technology will read the mail piece, reads the address and actually assigns that four-digit add-on to the mail piece and sprays the appropriate bar code onto the mail piece."  That bar code is what allows the post office to process, sort and present the mail to their carriers in walk sequence.

It’s hard to imagine now given its success, but when the ZIP code was first launched in July of 1963, it wasn’t mandatory, and it wasn’t immediately embraced. So a full-fledged marketing blitz was unleashed, complete with a mascot, Mr. ZIP.

And – for the hep cats - the Swingin’ Six.

It worked, in large part because the system worked. Not only did the ZIP code become universal, it grew into a phenomenon.

"Zip codes provide an identity," Powers said, pointing to the TV show Beverly Hills 90210 as just one example. And Marion pointed out that when growth in Williamsburg, Brooklyn recently forced the Post Office to add a second, new zip code for parts of that neighborhood?

"There was one fella who was interviewed in the paper and he was, 'Ah this is terrible, I’m gonna have to change my tattoo. And he rolled up his arm and had 11211 tattooed on his arm," she said.

And it’s not just the cultural piece. The 911 system is grafted over it. It’s crucial to the census. Marketers use it to target customers, political candidates to customize their message, economists and activists to build their case. All of it's possible thanks to the mail.

"All of those other applications are not something that anyone really understood to be a ramification," MArion said.

And yet …

"It works like a charm."

The Zoning Improvement Plan, better known as the ZIP code, launched in Massachusetts, and across the country, 52 years ago this week.

Some fun ZIP facts:

If you have a tale of forgotten Massachusetts history to share, or there's something you're just plain curious about, email Edgar at curiositydesk@wgbh.org. He might just look into it for you.