This document discusses IDL's support for the HDF file format. It provides a brief history of IDL, noting its origins at NCAR and NASA and long history supporting data analysis. It describes IDL's HDF support, which was introduced in version 4.0 and expanded in version 5.6 to include HDF5. The document outlines key HDF file reading and writing capabilities in IDL and new features added in version 6.3 like opaque, variable-length, enumerated, and compound data support. It positions IDL as a powerful tool for data visualization, processing, and analysis across platforms.