HIO

HIO may refer to:
 * Hillsboro Airport, in Washington County, Oregon, United States
 * Hypoiodous acid, an oxidising agent
 * Hybrid input-output algorithm, in coherent diffraction imaging
 * Oslo University College, the largest state university college in Norway
 * Østfold University College, a further and higher education institution in south-eastern Norway
 * Tsoa language, spoken in Botswana and Zimbabwe