Poor performance under a federal contract can have immediate consequences for contractors, who could be denied award or incentive fees, required to pay liquidated damages, or terminated for default. In addition, it could affect their ability to obtain future contracts because various provisions of federal law require agencies to evaluate contractors' "past performance" and consider past performance information when making source selection decisions in negotiated procurements and when determining whether prospective contractors are "responsible." "Past performance" refers to contractors' performance on "active and physically completed contracts." This book provides an overview of existing legal requirements pertaining to past performance, including the issues raised by contractors' attempts to challenge (1) agency evaluations of their past performance, (2) source selection decisions based, in part, on consideration of past performance information, and (3) responsibility determinations.