Irish ancient tales can be classified into four categories. It is worth noting that this classification is a modern concept.
- Mythological Cycle: the protagonists are the Síde
- Ulster Cycle: details the purportedly historical exploits of the Ulaid, a few centuries before and after the Christ
- Historical Cycle (or Kings Cycle): focuses on the activities of the "historical kings"
- Fenian Cycle (or Finn Cycle): describes the adventures of Finn mac Cumaill and his fíana
The limits between history and mythology are blurry, and tales from one category could also belong to another.