Horologium (Latin for "clock") may refer to:

• Clock, a device for measuring the time
• Astronomical clock, also sometimes distinguished as a horologium
• Horologium Augusti, a solar marker built in ancient Rome by Augustus, once believed to have acted as a sundial
• Horologium, a turret clock built in 1283 in Dunstable, UK
• Horologium Sapientiae ("Clock of Wisdom"), a 14th-century book on spirituality by Henry Suso
• Horologium Oscillatorium, a 17th-century book by Christiaan Huygens on pendulum clocks
• Horologium (constellation), in the southern celestial hemisphere named in honor of Huygens's work
• Horologium-Reticulum Supercluster, in the area of the constellation
• Horologium (Orthodoxy), or Horologion, the book detailing the prayers at the canonical hours in Eastern Orthodoxy

• Book of hours, a personal or Western Christian equivalent of the Eastern horologium
• Horology, the science of time-keeping
• Menologium