In his books Animal Intelligence and Mental Evolution in Animals, Romanes (1882/1906; 1884/1900) argued that apes, being phylogenetically close to humans, should be capable of intentional deception. Until recently, scientists have had little more than Romanes' faith and a few observations upon which to base an expectation of skill in intentional deception in apes (Mitchell, 1999). But in the past two decades, descriptions of deceptive behavior in apes and other nonhuman primates, as well as discussions of its psychological requisites, have become commonplace, lending greater support to the expectations of intentional deception by apes and of commonalities in the underlying mental states in humans and apes (see, e.g., Menzel, 1974; De Waal, 1982, 1986; Miles, 1986; Mitchell, 1986, 1993, 1997; Mitchell & Thompson, 1986a,c; Smith, 1987; Whiten & Byrne, 1988; Byrne & Whiten, 1990, 1992; Byrne, 1997). As might be expected on phylogenetic grounds, many deceptions used by humans in sports, play, and teasing (e.g., Mawby & Mitchell, 1986; Mitchell & Thompson, 1986b, 1993; LaFrenière, 1988; Leekam, 1991; Reddy, 1991; Mitchell, 1996) are strikingly similar to those used by nonhuman primates. Just as the signing skills of great apes are comparable to those of 2- to 3-year-old children (Brown, 1970; Savage-Rumbaugh et al., 1993; Miles, 1997; this volume; Parker & McKinney, in press), their deceptions are also sometimes similarly comparable (e.g., Reddy, 1991), but often great apes' deceptions seem much more skillful than those of even 4-year-old children (e.g., LaFrenière, 1988).