Treerecs: a tree reconciliation tool Treerecs is an open-source (species- and gene-) tree reconciliation software distributed under the GNU AGPL licence. It can correct, rearrange and (re-)root gene trees with regard to a given species tree. It was designed to be both efficient and easy to install and to use. Features - Correct gene trees with regard to a reference species tree - Root or re-root gene trees - Contract gene-tree branches whose support is lower than a given threshold, thus creating polytomies (multifurcations) that can be resolved therefater - Sample solutions with equivalent scores - Produce a graphical representation of the reconciled trees - Supported formats Treerecs supports the following formats: Newick, NHX, PhyloXML, recPhyloXML, SVG (graphical output). A program that can drive Treerecs, providing a GUI is Seaview, also available at SBo. The SlacBuild script builds two additional programs: 1) ALEevaluate_undated: an executable of the ALE (Amalgamated likelihood estimation, https://github.com/ssolo/ALE), by Szollosi GJ et al). This version has other mapping options and a different implementation in Bio++ use. 2) genetreeEditor: a small program which provides editing of gene names using species names and format conversion (Newick, Nhx or PhyloXML) .