<p>Candles flicker around ancestral shrines at a Day of the Dead vigil in a Mexican cemetery in this image, which haunted the cover of National Geographic in 1968.</p><p>Onlookers call upon the souls, "Salga—come out," during the Day of the Dead, a primarily Mexican holiday that lasts for one to three nights between October 31 and November 2. The holiday celebrates the dead through family gatherings like the one pictured above.</p><p>"The custom of bringing food and wine and candles and flowers to the graveyards is very much a part of Day of the Dead celebration," says Halloween historian <a href="http://www.people.fas.harvard.edu/%7Ebannatyn/">Lesley Bannatyne</a>, author of&nbsp;<em><a href="http://www.iskullhalloween.com/nation.html">Halloween Nation: Behind the Scenes of America's Fright Night</a>.</em></p><p>Both Day of the Dead and Halloween have Roman Catholic roots in All Saints' Day (November 1) and All Souls' Day (November 2). In Europe, All Saints' Day is also known as All Hallows, making October 31 All Hallows' Eve—the linguistic origin of "Halloween."</p><p>Before you get ready to trick-or-treat (or hand out the candy), enjoy these photos from our archives of Halloween and Day of the Dead celebrations. (Read more <a href="http://news.nationalgeographic.com/news/2011/10/111028-halloween-facts-costumes-history-nation-science/">Halloween facts</a>.)</p><p>—<em>By Becky Little, photo gallery by Nicole Werbeck and Sherry L. Brukbacher</em></p>