It's March 14, the day we irrationally celebrate the ratio of a circle's circumference to its diameter. Here's a roundup from our archive of what we know about pi.

We know pi appears when we talk about circles. But it appears in many other places, too. Why, pi, why?

This Pi Day we should celebrate William Jones, the 18th century Welsh farm boy who named the mysterious number.

Mathematicians have long been revealing the beauty in the one of nature's most mysterious numbers.

On international Pi Day it's time to look at Pi's position in unique formula that's praised much for its beauty in uniting several mathematical constants.

On the occasion of Pi Day, a look at the history of calculating the actual, and increasingly exact, value of pi (π).

3/14/15 on the calendar approximates the first five digits of the mathematical constant π. Math nerds will celebrate with baked goods, but π is a deeper, nobler entity.

The number pi (π = 3.14159265358979323846…), unique among the pantheon of mathematical constants, captures the fascination of the public and professional mathematicians. Three years ago one of the authors…

Some people have argued that Pi’s days are numbered and that other tools, such as tau, could do its job more efficiently. As someone who has studied Pi throughout his entire working life, my response to…