This paper starts with the hypothesis that Irish literature should be different from English literature in theme, feeling and the technique of expression. The differences the writer has found so far are as follows: the search for the father-omphalos, the personification of nature, the recognition of sex as an origin of creation, the search for aesthetics of darkness, the attachment to silence, the spirit of wandering, the cyclic view of the world and dramatic self-awareness, etc. Since the end of the 19th century, the Irish writers’ strong attachment to their own tradition has been expressed as their reaction to a sense of lack as reflected in terms such as “center,” “omphalos,” and “search for father.” This phenomenon accounts for the birth of Irish national literature. From Oscar Wilde and Bernard Show in the 19th century to the recent poet, Seamus Heaney, they tried to deanglicize and create their own literature. But through this process, they have not neglected the chance to become a master of the international literature, by using the language of enemy. And each writer has a peculiar method of deanglicizing. For example, Oscar Wilde and Bernard Show who contributed to cosmopolitanism of modern Irish literature attacked and illuminated the English audiences by the reversing play-role. Understanding the enhanced nationalism, W.B. Yeats and other revivalists of Irish literature integrated English culture and tradition into the nationalistic movement. This is why their works were called “the cracked glass of the servants.” J. Joyce and other modernists, in a genuine sense, sought for their original nationality and to do this, they tried to recognize the picture of themselves as paralysis. From the establishment of the Irish Republic to the recent, strong nationalism and internationalism, as it has grown as one of the European countries, have been reconciled. Modern Irish literature has succeeded in regaining its own tradition and reaching top as one of the international literatures, getting through the five phases. During the first phase it showed the spirit to reverse the English cultural system and value by preempting the role of the English. The second phase is the period when they stimulated the national feeling and praised national heros. At the third phase modernists including Joyce, Kinsella, and Clarke attacked the nationalism of the second phase, saying that it was like a bubble full of the imagination the English wanted, and they exposed the realistic viewpoint of Irish life to their literary works. The fourth phase shows the reconciliation between parochialism of P. Kavanagh and cosmopolitanism of J. Montague. The fifth phase shows that with the enforcing of nationalism caused by the Ulster Trouble, harmony of nationalism and internationalism has been sought. The most important element that has led modern Irish literature to the top level is the spirit of omphalos through their confidence in their own culture and the sense of lack, and thereby the attachment to losses in language, land and tradition. Besides these, modern Irish writers haveoriented from the early period the Irish Republic towards an international country. The harmony of regionalism and cosmopolitanism, as well as that of individual interests and community interests, has led the Irish Republic to become one of the best postcolonial countries and cultural models.