Halloween: etymology of the name
The name Halloween (Irish Hallow E'en), derives from the contracted form of All Hallows' Eve, where Hallow is the archaic English word meaning Holy The eve of All Saints, then. All, however, English is All Hallows' Day. The importance, however, is on the eve can be deduced from the value of cosmology Celtic This conception of time, albeit only formally and linguistically speaking, is very involved in English-speaking countries, where several festivals are accompanied by the words "Eve" including the same Eve, "New Year's Eve, or the night of Christmas" Christmas Eve ".

The Celts and the celebration of Samhain
The Celts were a people of mainly pastors, unlike other European cultures, such as those of the Mediterranean basin. The rhythms of their lives were thus marked by delays cattle imposed, different times from those camps.

At the end of the summer, the shepherds returned to their flocks valley, prepare for the arrival of winter and the beginning of the new year. For the Celts, in fact, the new year will not begin on 1 January as for us today, but on 1 November, when the season ended officially began warm and the season of darkness and cold, as long as there are closed home for many months, sheltering from cold, building tools and spending their evenings telling stories and legends.

The transition from summer and the winter from the old to the new year was celebrated with long celebrations, the Samhain (pronounced sow-in where sow ago rhymes with cow), which derives from the Gaelic samhuinn and means "summer's end" the end of the summer. In Ireland, the feast was known as Samhein, or La Samon, the Feast of the Sun, but the concept is the same.
At that time of the fruits of the fields (which although not the main activity of the Celts, were still cultivated) were insured, the cattle had been well fed fresh air and pastures and mountains of stocks for the winter they were prepared. The community, therefore, could rest and thank the Gods for their generosity. This was through the Samhain, which also served to exorcise the arrival of winter and its dangers, uniting and strengthening the community through a rite of passage that coud make propicious the benevolence of the gods.

The importance that Celtic people attributed to Samhain resides in their conception of time, seen as a circle divided into cycles: the end of each cycle was considered very important and full of magic. Together with Samhain (Oct. 31, precisely) is celebrating Lughnasadh (1 August), Beltaine (May 1), Imbolc (1 February), Yule (21 June), Ostara (22 September), Litha (December 22) and Mabon (21 March).
The advent of Christianity has not entirely erased these festivities, but in many cases it was superimposed them giving their contents and meanings different from the original.

The death was the main theme of the festival, in line with what was happening in nature during the winter season life seems to be silent, while in reality renews itself underground, where traditionally, among other things, the rest dead. Hence it is understandable the combination of Samhain worship of the dead.
The Celts believed that on the eve of every new year, that is October 31, Samhain called him all the spirits of the dead, who lived in a land of eternal youth and happiness called Tir nan Oge, and that the forces of spirits could join the the world of the living, causing in this way, the temporary disappearance of the laws of time and space and making sure that what comes after is merged with the world of the living and allowing wandering spirits roam undisturbed on Earth.

Samhain was, therefore, a celebration that united the fear of death and spirits with the fun of celebrations for the end of the old year. During the night of October 31 held meetings in the woods and hills for the ceremony Behavior of the Sacred Fire and animal sacrifices were made. Dresses with grotesque masks, the Celts returning to the village, taking with light lanterns carved consist of onions which were placed inside the embers of the Sacred Fire. After these rites the Celts celebrated for 3 days, masking themselves with skins of animals killed to frighten the spirits.
In Ireland spread the habit of turning flashlights and torches outside the doors and leave food and milk for the souls of the dead which would have made access to their families, so that they could revive and decide not to make jokes living.

The advent of Christianity
Through the Roman conquests, Christians and Celts were in contact. Evangelization of the British Isles brought with it a new concept of life, far from the Celtic and during that period the Church tried to eradicate the pagan cults, but not always succeeded. Halloween was not completely erased, but was somehow christianized through the establishment of the days of All Saints on 1 November and then the commemoration of the dead on 2 November.
It was Odilone of Cluny, in 998 d.C., to give the boot to what was a new and longeval tradition of Western societies. Then he gave provision so that monasteries employees from the abbey celebrated the rites of the dead as of vespers on 1 November. The following day was willing to be commemorated with an Eucarestia offered to the Lord, pro requie omnium defunctorum. That is an spread quickly throughout Christian Europe to go to Rome later.
The Feast of All Saints, in fact, was celebrated for the first time in Rome on 13 May 609 d.C., at the Pantheon of consecration to the Virgin Mary. Later, Pope Gregory III established that the Feast of All Saints was celebrated rather than on 13 May, but the 1st November, as happened some time ago in France. It was about the ninth century d.C. The Feast of All Saints was officially institutionalized and then extended to the whole Church through the work of Pope Gregory IV.
With the exception of Orthodox Christians, who consistently with the first celebrations, still celebrate All Saints in the spring, the Sunday after Pentecost.
The influence of the cult of Samhain was not, however, eradicated, and for this reason the Church added, in the tenth century, a new festival: 2 November, Day of the Dead, dedicated to the memory of the souls of the missing.

From Ireland to the United States
Towards the middle of the nineteenth century, Ireland was seized by a terrible famine, still remembered with great participation from Ireland. In that period to escape poverty, many people decided to leave the island and tentar fortune in the United States, where he created, like many other nationalities, a strong community. Inside it were kept alive the traditions and customs of their homeland, and among them 31 October was celebrated Halloween.
Soon, this practice is widespread throughout the American people, becoming almost a national holiday.
More recently, the United States thanks to the movies and television have exported all over the world celebrate Halloween, affecting that part of Europe which had remained outside. In many films and television often portray the famous pumpkin and masked children who knock at the door. And many, finally, are the books and horror stories that take Halloween as wallpaper or as a starting point of their plots.
In the United States, Halloween has lost its meaning and religious rituals, and has become an occasion for fun and organize expensive and cheerful festivities. It seems that every year Americans spend two and a half million dollars in costumes, decorations and parties for the October 31!