Like the Celtic traditions of Samhain, which were also associated with the end of the year and the last harvest festival, it was believed that at this time of the year the souls of the departed can return to visit the living (the "veils are thin"). It is not a time of mourning since, as the Latin saying goes, "the path back to the living world must not be made slippery by tears".
Celebrations for the dead originated in indigenous Mexico before the Spanish conquest. Following the Spanish conquest of Mexico during the 16th century there was a blending of indigenous customs with the new Catholic religion. All Saints' Day and All Hallows Eve (Halloween) roughly coincided with the preexisting Día de Los Muertos resulting in the present day event. Although the skeleton is a strong symbol for both contemporary Halloween and los Días de Los Muertos, the meaning is very different. For Días de Los Muertos the skeleton is not a scary or macabre symbol at all, but rather represents the dead playfully mimicking the living.
Very often, a large community altar may include many small personal shrines, such as the one below that includes Frieda Kahlo.
Preparation begins weeks in advance when statues, candies, breads and other items to please the departed are sold in markets. A sweet bread, pan de muerto, with decorations representing bones is very popular, as are sugar skulls made from casts. All sorts of art objects and toys are created. This gives the economy a boost in much the same way as our Christmas season does. Alters ofrecetas (offerings) are set up in the home with offerings of sweets and fruits, corn and vegetables, as well as the favorite foods and beverages of the deceased. It's not unusual to see a good cigar and whiskey bottle beside a photograph of a loved one. These offerings may later be given away or consumed by the living after their "essence", and the loving remembrance, has been enjoyed by the dead. Marigolds are the traditional decorative flower.
The particulars of the celebration vary widely. On November 1, Día de Muertos Chiquitos, the departed children are remembered. The evening is sometimes called la Noche de Duelo, The Night of Mourning, marked by a candlelight procession to the cemetery. On November 2, Día de los Muertos, the spirits of the dead return. Entire families visit the graves of their ancestors, bringing favorite foods and alcoholic beverages as offerings to the deceased as well as a picnic lunch for themselves. Traditionally there is a feast in the early morning hours of November 2nd although many now celebrate with an evening meal.
There are sugar skulls and toys for the children, emphasizing early on that death is a part of the life cycle, and the importance of remembering those who have passed on to another kind of life.