The concept of the mole was first developed by Amedeo Avogadro, an Italian scientist, in 1811. Avogadro proposed that equal volumes of gases, at the same temperature and pressure, contain an equal number of particles (molecules or atoms). This idea, known as Avogadro's law, laid the foundation for the mole concept.

However, it wasn't until 1967 that the mole was officially defined and adopted as the standard unit for measuring the amount of substance. This definition was established by the International Union of Pure and Applied Chemistry (IUPAC), which defined the mole as the amount of substance containing exactly 6.02214076 × 10²³ particles (atoms, molecules, ions, or electrons). This number, known as the Avogadro constant (Nₐ), represents the number of particles present in 12 grams of pure carbon-12 (¹²C).