1,000,000,000 (one billion, short scale; one thousand million or milliard, long scale) is the natural number following 999,999,999 and preceding 1,000,000,001.

In scientific notation, it is written as 10⁹.

A billion traditionally equated to one million, million, (1,000,000,000,000) though the short scale (American English) billion of merely one thousand million (1,000,000,000) has been adopted in finance and increasingly in other fields. The unambiguous term thousand million has the same meaning in both scales.

In South Asian English, it is known as 100 crore or 1 arab.

The term milliard can also be used to refer to 1,000,000,000; this name very often appears in other languages.

This terminology is rarely used in English outside of British English. The SI prefix giga indicates 1,000,000,000 times the base unit.

See Orders of magnitude (numbers) for larger numbers; and long and short scales.

The facts below give a sense of how large 1,000,000,000 (10⁹) is in the context of time according to current scientific evidence:

One million (1,000,000) or one thousand thousand, is the natural number following 999,999 and preceding 1,000,001. The word is derived from the early Italian millione (milione in modern Italian), from mille, "thousand", plus the augmentative suffix -one.

In scientific notation, it is written as 1×10⁶ or just 10⁶.Physical quantities can also be expressed using the SI prefix mega, when dealing with SI units. For example, 1 megawatt equals 1,000,000 watts.

The meaning of the word "million" is common to the short scale and long scale numbering systems, unlike the larger numbers, which have different names in the two systems.

The million is sometimes used in the English language as a metaphor for a very large number, as in "Never in a million years" and "You're one in a million", or a hyperbole, as in "I've walked a million miles" and "You've asked the million-dollar question".

Even though it is often stressed that counting to precisely a million would be an exceedingly tedious task due to the time and concentration required, there are many ways to bring the number "down to size" in approximate quantities, ignoring irregularities or packing effects.