Abstract—The problem of merging k (k≥ 2) sorted lists is considered. We give an optimal parallel algorithm which takes $O({\textstyle{{n\log k} \over p}}+\log n)$ time using p processors on a parallel random access machine that allows concurrent reads and exclusive writes, where n is the total size of the input lists. This algorithm achieves O(log n) time using $p={\textstyle{{n\log k} \over {\log n}}}$ processors. Most of the previous research for this problem has been focused on the case when k = 2. Very recently, parallel solutions for the case when k > 2 have been reported. Our solution is the first logarithmic time optimal parallel algorithm for the problem when k≥ 2. It can also be seen as a unified optimal parallel algorithm for sorting and merging. In order to support the algorithm, a new processor assignment strategy is also presented.