In Old English poetry a coordinate conjunction and is used at significant frequency as a constituent of the X and Y-construction. From the results of our examination into the X and Y-construction in The Battle of Maldon and Beowulf, it was revealed that the number of this construction that is placed in the a-verse of a long line is large and in most cases the word placed in the position of X alliterates with that placed in the position of Y, that is to say, double alliteration is provided in the long line. On the other hand, there are few cases where the construction is set in the b-verse or the word in the position of X does not alliterate with that in the position of Y even though the construction occupies the a-verse. We regard these kinds of instances as marked and presume, on the basis of our survey on the construction in The Battle of Maldon and Beowulf, that exceptional examples can be found where both the positions of X and Y of the construction are gotten by proper nouns or can be caused by making oral-formulaic expressions. We therefore conclude that the X and Y-construction in Old English poetry must be a writers' poetic device with which to produce double alliteration.