In this paper, we generalize the proximal point algorithm to complete CAT(0) spaces and show that the sequence generated by the proximal point algorithm $w$-converges to a zero of the maximal monotone operator. Also, we prove that if $f: Xrightarrow ]-infty, +infty]$ is a proper, convex and lower semicontinuous function on the complete CAT(0) space $X$, then the proximal...