The Working Party on international nuclear data Evaluation Cooperation (WPEC) is a collaborative effort between the major OECD nuclear data projects: ENDF/B (USA), JENDL (Japan) and JEFF (Europe), and the IAEA- supported non-OECD projects CENDL (China) and BROND (Russian Federation). Nuclear data challenges and problems that are common to all projects are considered in various WPEC subgroups that are normally of limited time span. The achievements of these subgroups during the course of 2005/06 are reviewed in this paper. Among the recent accomplishments are improved criticality predictions through revised U evaluations, the completion of new cross-section standards, and the creation of a new fission product library. Problems that are currently being addressed are the processing and inclusion of covariance data in the libraries, improvements in decay data to assist in decay heat calculations, assembly of a well-structured High Priority Request List, validation of the new fission product cross-section library, and the assessment of nuclear data needs for GEN-IV.