Madam, we are here for the usual purpose, 'trick or treat.'
(«The Gangsters of Tomorrow», The Helena Independent, November 2, 1934)

On November Eve they are at their gloomiest, for, according to the old Gaelic reckoning, this is the first night of winter. This night they dance with the ghosts, and the pooka is abroad, and witches make their spells, and girls sit at a table with food in the name of the devil, that the fetch of their future lover may come through the window and eat of the food.
(from 'Fairy and Folk Tales of the Irish Peasantry',1888 by William Butler Yeats, the Irish poet)

Halloween (first used in the 16th century) or All Hallows' Eve  ('Evening'), holy or hallowed evening observed on October 31, the eve of All Saints' Day or the night before All Hallows' Day. The feasts of Hallowe'en, or All Hallows' Eve and the devotions to the dead on All Saints' and All Souls' Day are both mixtures of old Celtic, Druid and other heathen customs intertwined with Christian practice. In the case of Halloween, the Celtic celebration of Samhain is critical to its pagan legacy.

Historian Nicholas Rogers, exploring the origins of Halloween, notes that while «some folklorists have detected its origins in Roman feast of Pomona, the goddess of fruits and seeds, or in the festival of the dead called Parentalia, it is more typically linked to the Celtic festival of Samhain» — the Old Irish for «summer's end».

Samhain (pronounced sah-win or sow-in) heralds the beginning of the Celtic New Year. It was the first and most important of the four quarter days in the medieval Gaelic (Irish, Scottish and Manx) calendar. It was held on or about October 31 – November 1 and marked the end of the harvest season and the beginning of winter or the 'darker half' of the year. This was a time for stock-taking and preparing for the cold winter ahead; cattle were brought back down from the summer pastures and livestock were slaughtered. In much of the Gaelic world, bonfires were lit and there were rituals involving them. Some of these rituals hint that they may once have involved human sacrifice. Divination games or rituals were also done at Samhain.

It is the time when Celts believed the gates to the otherworld were opened and they could communicate with the dead. It was thought that at the feasts of Samhain and Beltaine (May 1st), supernatural events took place. Some believe Samhain is the time the fairy mounds open and the   Sidhe (pronounced «Shee») fairies swarm. On this evening, it was customary to leave a milk and barley offering for the Sidhe. It was a dangerous time to be abroad at night for fear of abduction by the Sidhe as they traveled around the countryside. Even today, some rural Irish people will tell that the moan of the bean Sidhe ( «banshee») foretells of a death in a family by morning.

Feasting and merrymaking played a big part in rural homes. The mistress of the house prepared a special feast in honor of the night.   Colcannon*, a mashed potato and kale or cabbage dish with a reservoir of creamy melted butter, was a favorite. Boxty bread*, made from mashed potatoes and flour was also popular, as was Barm Brack.

*Colcannon (Irish: cál ceannann, meaning «white-headed cabbage») is a traditional Irish dish mainly consisting of mashed potatoes with kale or cabbage. At one time it was a cheap, year-round staple food, though nowadays it is usually eaten in autumn/winter, when kale comes into season.

The recipe advises to mix the mashed potatoes in with chopped cooked kale, green onions (scallions, leeks, onions and chives), milk or cream, and lots of butter. To serve one makes a depression in the middle of the mashed potatoes and puts a knob of butter in it. To eat it, you dip a forkful of the potatoes in the melted butter. It is often eaten with boiled ham or Irish bacon. An old Irish Halloween tradition is to serve colcannon with a ring and a thimble hidden in the fluffy green-flecked dish. Prizes of small coins such as threepenny or sixpenny bits were also concealed in it.

«Did you ever eat Colcannon, made from lovely pickled cream?
With the greens and scallions mingled like a picture in a dream.
Did you ever make a hole on top to hold the melting flake
Of the creamy, flavoured butter that your mother used to make?»

The chorus:

«Yes you did, so you did, so did he and so did I.
And the more I think about it sure the nearer I'm to cry.
Oh, wasn't it the happy days when troubles we had not,
And our mothers made Colcannon in the little skillet pot.»

(from a traditional Irish song «Colcannon», also called «The Skillet Pot»)

*Boxty (bacstaí or arán bocht tí in Irish meaning «poor-house bread») is a traditional Irish potato pancake. The dish is mostly associated with the north midlands, north Connacht and southern Ulster, in particular the counties of Mayo, Sligo, Donegal (where it is known locally as poundy or poundies; also known as potato bread in Ulster), Fermanagh, Longford, Leitrim and Cavan. There are many recipes but all contain finely grated, raw potatoes and all are served fried.

The most popular version of the dish consists of finely grated, raw potato and mashed potato with flour, baking soda, buttermilk and sometimes egg. The grated potato may be strained to remove most of the starch and water but this is not necessary. The mixture is fried on a griddle pan for a few minutes on each side, similar to a normal pancake. Traditional alternatives include using only raw potatoes, boiling it as a dumpling or baking it as a loaf.

Boxty on the griddle,
And Boxty on the pan;
The wee one in the middle
Is for Mary Ann.
Boxty on the griddle,
boxty on the pan,
If you can't bake boxty
sure you'll never get a man.
Boxty on the griddle,
Boxty on the pan,
If you don't eat boxty,
You'll never get a man.

(from an Irish folk rhyme)