Akira Sakai Mean-field Critical Behavior for Contact Processes (328K, .ps.gz) ABSTRACT. We prove the triangle condition for the basic contact process in sufficiently high dimensions and for the spatially spread-out contact process in spatial dimension $d > 4$. Combining with the result of Barsky and Wu in 1998, we prove the mean-field critical behavior for these processes. Our results imply that the upper critical dimension for the contact processes is four.