BUCKy: Gene tree/species tree reconciliation with Bayesian concordance analysis. Motivation: BUCKy is a C++ program that implements Bayesian concordance analysis. The method uses a non-parametric clustering of genes with compatible trees, and reconstructs the primary concordance tree from clades supported by the largest proportions of genes. A population tree with branch lengths in coalescent units is estimated from quartet concordance factors. Availability: BUCKy is open source and distributed under the GNU general public license at www.stat.wisc.edu/∼ane/bucky/.