511 may refer to:

• The year 511 AD of the Common Era
• The year 511 BC before the Common Era
• The number 511 (number)
• The telephone number 5‒1‒1, used for transportation information in many regions of Canada and the United States of America
• 511 keV, the energy of each of the two photons created when a positron and an electron annihilate

• All pages with titles beginning with 511
• All pages with titles containing 511
• 51 (disambiguation)