Happy Pi Day! Today’s date is 3.14, the first three digits of arguably the most famous mathematical constant (anyone remember e? Napier’s constant? Didn’t think so). School children and geeks everywhere are celebrating it today by, well, eating pies, as it turns out.

Pi Day was created in 1988 by Larry Shaw at the San Francisco Exploratorium as an entertaining way to get kids interested in math. The first celebration was nothing more than a circular walk around the main hall of the museum ending at a big table of pies. That walk was used to illustrate the ratio that pi represents: the circumference of a circle divided by its diameter.

That simple equation has lead to increasingly complicated and elegant ways to divine its meaning. More than a few mathematicians have labored over trying to find patterns in its infinite string of digits, convinced there is a message in the math. Others spend their time attempting just to memorize as much of it as they can.

It’s fundamental throughout the field of mathematics, not just in geometry or trig. Used by everyone from oceanographers to economists, we can find it in the measurements of the Great Pyramid and in popular culture, in movies and TV shows. It even appears twice in the Bible.

So go out tonight for pizza or order a slice of pie for dessert and celebrate the circle. Happy Pi Day!