The 2005–06 Celtic League was the fifth Celtic League season, and the third following the introduction of regional rugby in Wales. Eleven teams, from three countries participated. The final table was dominated by the Irish, with the top three spots taken by Ulster, Leinster and Munster respectively. The 2005–06 season was the first (and last) season for which the "free weekend" was awarded points for. Due to the odd number of teams participating, for every round of fixtures, one team has a so-called "free weekend". Each time this occurred, the team was awarded four points, so although at the end of the season it did not alter the positions (each team has a guaranteed 8 points), the table is skewed during the season according to the fixtures.