The set of physical quantities that play a fundamental role in basic physical theories, primarily at the atomic and subatomic levels, including also those quantities that provide the connection between microscopic physics and the macroscopic world. Examples of fundamental constants are the velocity of light in vacuum c; the Planck constant h; the universal gravitation constant G; the electron charge e; the masses of the proton, the neutron, and the electron, m_p, m_n, and m_e; the Boltzmann constant k; and the Avogadro constant N_A; as well as any physical constant such as the fine-structure constant α that is a combination of these constants.