R package ACTCD: Asymptotic Classification Theory for Cognitive Diagnosis. This package includes functions used to perform cluster analysis for cognitive diagnosis based on the Asymptotic Classification Theory (Chiu, Douglas & Li, 2009). Given the sample statistic of sum-scores and the item-by-attribute association matrix (Q-matrix; Tatsuoka, 1985), cluster analysis techniques can be used to classify examinees into latent classes based on their attribute patterns. In addition to the algorithms used to classify data, three labeling approaches are proposed to label clusters so that examinees’ attribute profiles can be obtained.