Euclid (named after the ancient Greek mathematician Euclid of Alexandria, the "Father of Geometry"), is a space mission currently under development by the European Space Agency (ESA). The objective of Euclid is to better understand dark energy and dark matter by accurately measuring the acceleration of the universe. To achieve this, the spacecraft will measure the redshift of galaxies at varying distances from Earth and investigate the relationship between distance and redshift. Dark energy is generally accepted as contributing to the increased acceleration of the expanding universe, so understanding this relationship will help to refine how physicists and astrophysicists understand it. Euclid's mission advances and complements ESA's Planck mission, and other contemporary space missions.