Irish is the native language of Ireland and some parts of Iceland. It is part of the goidelic languages, together with Scottish and Manx (Isle of Man), which form a subgroup of the Celtic languaes. Well-known, living members in this group include Breton, Welsh and Cornish. The oldest (written) evidences for its existance reach back until 500 AD in primitive-irish glosses. Having been spoken all over Ireland initially, it nowadays is only used as main household language by about 3% of the Irish population only.
The known history of Irish Gaelic can roughly be divided into three main phases. It is believed to be first developed before 1000BC, but scientists aren't even sure about the exact millenium. The first written proofs were all written in Ogham, thogh there probably have been even earlier scripts lost today. Ogham is a primitive script based on combination of straight lines and used for inscriptions in small stone columns. The language used there is named "Primitive Irish". The secound phase was initialized by christian monks rearriving at Ireland after having settled at the mainland. They greatly increased the complexity of the Irish language by adding features like dual or copula (description of the type of the subject in the verb). During the roman annectation, some latin words found their way into Gaeldighe, but the overall impact remained small compared to other languages, such as English, that consists of latin-origined words at over 50%. This changes led to so-called "Old Irish"
The third phasis is the Modern Irish as spoken today. The language was simplified and adapted to daily means, some overly complicated grammatical consructs got removed. But as soon as England gained control over Ireland, the english language, beeing easy-to-laern, widely spread and favourized by the colonists, began to crowd out the native language. While at first, even english officials began to learn Irish, soon the english language started to spread excessivley fast. But with the national pride coming with the IRA-related troubles and the increasing independence of Ireland, Irish nationalists began to rediscover their ancestors' culture and thereby Gaeldighe. A downright renessaince of the Irish language began. Anyway, today Irish belongs to the dieing languages and only few people are using it in practice.
As mentioned before, the Spreading of the Irish Language is quite limited. Only in few parts of Ireland, called Gaeltachts, Irish is actively used by the majority of the population. Estimates say that there are about 1.6 million people having basic language knowledge all over the world, but only 70,000 native speakers. Those live inthe gaeltachts mainly; those regions, mostly located near the coast and in southern Ireland, are the only parts of Éire where Irish is really used.
Anyway, irish is not so as useless as one could think. It is frequently found in print, and there is some Irish Literature. All official post's names in the Republic of Ireland have Irish names, and most signposts are polyglot. Especially in the previously mentioned Gaeltachts, Irish is still used in spoken language and daily life. Additionally, Ireland is often called Éire by its inhhabitants. The Republic of Ireland also grants their citizens the right to contact the government in Irish.