Eugenia (minor planet designation: 45 Eugenia) is a large asteroid of the asteroid belt. It is famed as one of the first asteroids to be found to have a moon orbiting it. It was also the second triple asteroid to be discovered, after 87 Sylvia.

Eugenia was discovered on 27 June 1857 by the Franco-German amateur astronomer Hermann Goldschmidt.^[12] His instrument of discovery was a 4-inch aperture telescope located in his sixth floor apartment in the 6th Arrondissement of Paris.^[13] It was the forty-fifth minor planet to be discovered. The preliminary orbital elements were computed by Wilhelm Forster in Berlin, based on three observations in July, 1857.^[14]

The asteroid was named by its discoverer after Empress Eugenia di Montijo, the wife of Napoleon III.^[12] It was the first asteroid to be definitely named after a real person, rather than a figure from classical legend.^[15]

Eugenia is a large asteroid, with a diameter of 214 km. It is an F-type asteroid, which means that it is very dark in colouring (darker than soot) with a carbonaceous composition. Like Mathilde, its density appears to be unusually low, indicating that it may be a loosely packed rubble pile, not a monolithic object. Eugenia appears to be almost anhydrous.^[16] Lightcurve analysis indicates that Eugenia's pole most likely points towards ecliptic coordinates (β, λ) = (-30°, 124°) with a 10° uncertainty,^[6] which gives it an axial tilt of 117°. Eugenia's rotation is then retrograde, rotating backward to its orbital plane.

• Dactyl and Ida, another asteroid and asteroid moon system catalogued by astronomers
• Florence, another dual-moon asteroid confirmed only in September 2017.