Since Ernst Windisch’s monumental edition of the Táin Bó Cúailnge in 1905, a number of theories have been launched to explain how this central epic of Irish literature came into being, but still Celticists have not come to grips with the (various versions of the) work itself. However important the orality-literacy debate and matters like the mentality (Weltbild ) of early medieval Ireland and the functioning of early Irish literature in its European context are, these problems do not absolve Celticists from taking a close look at the texts themselves. In this paper I shall try to answer the following two questions : (1) What does the structure (Bauplan ) of the oldest version of the Táin teach us about the genesis (Entstehungsgeschichte ) of the work ? ; (2) what was the relation between the Táin and the matter of Ulster as a whole ?