There are 2 tests looked at in determining whether an individual is resident. If either tests is satisfied the individual is resident.
Firstly you look at the days present in Ireland in the tax year concerned and if greater than 183 days the individual is resident.
If the 183 day test is not satisfied, then you must look at the number of days present in Ireland in the tax year concerened and the immediately preceding tax year. If the total number of days exceeds 280 the individual is resident. Therefore, in determining whether an individual is resident in 2009 you would count up days in 2009 and 2008 and if they exceed 280 the individual is resident in 2009.
An execption to the 280 day test applies where the individual is in Ireland for less than 30 days in the tax year concerned. Therefore again looking at 2009, if the individual was present in Ireland for 270 days in 2008 and 15 days in 2009, the 280 days test would be met but as the individual was present for less than 30 days in 2009 they would not be resident for that year.