Remnants of the mythology of pre-Christian Ireland are preserved in medieval Irish literature, its characters largely euphemised and its religious significance suppressed by its Christian redactors. The surviving material has come to be grouped in four cycles:
- the Mythological Cycle, which includes origin myths and stories of the presumed gods of the Irish;
- the Ulster Cycle, legends of the heroes of the Ulaid set around the 1st century AD;
- the Fenian Cycle, tales of the hero Fionn mac Cumhaill and his warriors, set around the 3rd century AD;
- the Historical Cycles, also known as the Cycles of the Kings, a portmanteau category containing legendary tales of the kings of Ireland.
There are also a number of stories which do not fit comfortably into any of the cycles.
Irish mythology was extensively drawn upon by many of the authors of the Irish literary renaissance.