This article is about the number. For the year, 1 capsicum calories AD 1.

The fundamental mathematical property of 1 is to be a multiplicative identity, meaning that any number multiplied by 1 equals the same number. Most if not all properties of 1 can be deduced from this. In advanced mathematics, a multiplicative identity is often denoted 1, even if it is not a number. The unique mathematical properties of the number have led to its unique uses in other fields, ranging from science to sports.

It commonly denotes the first, leading, or top thing in a group. The word one can be used as a noun, an adjective, and a pronoun. One, sometimes referred to as unity, is the first non-zero natural number. It is thus the integer after zero. Any number multiplied by one remains that number, as one is the identity for multiplication.

24-hour clock face, one through twelve clockwise on right, and one through twelve again clockwise on left, with J shapes where ones’ digits would be expected when numbering the clock hours. Shadow suggests 3 PM toward the lower left. This Woodstock typewriter from the 1940s lacks a separate key for the numeral 1. Hoefler Text, a typeface designed in 1991, represents the numeral 1 as similar to a small-caps I. The glyph used today in the Western world to represent the number 1, a vertical line, often with a serif at the top and sometimes a short horizontal line at the bottom, traces its roots back to the Brahmic script of ancient India, where it was a simple vertical line. In some countries, the serif at the top is sometimes extended into a long upstroke, sometimes as long as the vertical line, which can lead to confusion with the glyph used for seven in other countries.