Cúng cô hồn draws on two separate religious traditions that arrived in Vietnam from China and merged, over centuries, into a single distinctly Vietnamese folk practice — one now sustained less by temples than by shopkeepers.
According to Taoist belief, the King of Hell orders the Ghost Gate (Quỷ Môn Quan) opened on the 2nd day of the 7th lunar month, freeing hungry, unclaimed spirits to wander the earth until the gate closes again on the 15th day, sending them back.
A parallel tradition traces to the story of Mục Kiền Liên (Maudgalyayana), a disciple of the Buddha who rescued his mother from the realm of hungry ghosts by organizing an offering ceremony with the monastic community — the origin of Vu Lan, Vietnam's Buddhist festival honoring parents, observed on the same 15th day of the 7th lunar month.
Over time, Vietnamese folk religion merged these two traditions into a single practice: offerings of food, incense and small gifts left out for cô hồn — wandering souls who died suddenly, violently, or without descendants to tend their graves, and who are believed to go hungry and occasionally cause mischief as a result.
Beyond the 7th lunar month, many Vietnamese households and businesses — particularly in the south — perform a smaller version of the ritual twice every lunar month, on the 2nd and the 16th; in central and northern Vietnam, the equivalent dates fall instead on the 1st and the 15th, tied to the new and full moon.
For many shopkeepers, the monthly offering has become less about the 7th lunar month specifically and more a routine act of commercial insurance — a small, recurring gesture meant to keep wandering spirits from disturbing trade and to invite good fortune into the shop for the two weeks ahead.