In the bicentenary year of Darwin's birth, the American Society of Primatologists honored his memory by convening a symposium entitled “Understanding emotions in primates: In honor of Darwin's 200th birthday.” The four articles in this special section, excepting this introduction, derive from that symposium. The section confirms that the topic of emotion is once again, as in Darwin's lifetime, the subject of wide-ranging, theoretically exciting research, and that studies with nonhuman primates are at the leading edge of a rapidly changing field. Am. J. Primatol. 73:503–506, 2011. © 2011 Wiley-Liss, Inc.