Peanut rust, caused by Puccinia arachidis Speg, is an important foliar disease of peanut (Arachis hypogaea L.) in tropical countries. The best option for disease management is host resistance. The objectives of this project included characterizing peanut genotypes for resistance to P. arachidis, assessing the genetic variation of newly developed Collaborative Research and Support Program (CRSP) peanut breeding lines, and assessing genetic variability among P. arachidis populations. In field studies conducted over 2010-2011, several CRSP breeding lines demonstrated varying levels of rust resistance. Detached leaf assays were used to examine the components of resistance to P. arachidis. Few significant differences were observed in these studies. We used SSR markers to characterize newly developed CRSP breeding lines, plant introductions, and commonly grown cultivars. The SSR markers used detected polymorphisms but were not able to distinguish resistant from susceptible peanut genotypes. Sequences of the 5.8S-ITS2-28S region of P. arachidis isolates collected from different regions in the United States and other countries do not indicate high genetic variability among the populations. Accepted for publication 23 September 2013. Published 25 November 2013.