Quote Originally Posted by firefytr
=IF(SUMPRODUCT(--(YEAR(A2:A10)=2006))=COUNT(A2:A10),"Yes","No")

Of course you would need to define the year (2006 in this example) and it assumes a range of only A2:A10.

Is the year defined here, or are you looking for any difference?
Use the year of the first cell in the range

=IF(SUMPRODUCT(--(YEAR(A2:A10)=YEAR(A2)))=COUNT(A2:A10),"Yes","No")