Traditionally they were religious events, first introduced by Spanish friars evangelizing to indigenous people. The posadas taught the story of Jesus’ birth in Bethlehem through song, nativity scenes and nine days of Masses. Eventually, over the course of a few hundred years, the posadas moved from the churches into people’s homes and neighborhoods. Today, the posadas have mostly become private parties that mix some religious elements with food and drinks. A piñata is a must, as are tamales, ponche and buñuelos.
If you want to throw your own Mexico-style posada, here’s a list of the elements to include. And if you don’t feel like cooking, no worries—posadas can be done potluck-style.