The Data Records produced by NPP and NPOESS will be delivered to users packaged in Hierarchical Data Format (HDF) using a consistent NPOESS profile. This data format is different from heritage data formats. HDF is a cross-platform data format and applications programming interface (API) originally developed for use in high performance computation environments at the National Center for Supercomputing Applications (NCSA) at the University of Illinois Urbana-Champaign (UIUC). HDF is now supported by a not-for-profit organization "The HDF Group". Because all NPOESS Data Records will use the same profile conventions, user and applications that understand how to read one NPOESS data product will be able to read other products. This presentation will describe HDF and the NPOESS profile of HDF5.