HDI may refer to:

• Human Development Index, a United Nations measure of well-being in a country
• PSA HDi engine, a diesel automobile engine by Peugeot/Citroën
• Hexamethylene diisocyanate, an organic compound used to make polymers such as polyurethane
• HDi Interactive Format (formerly iHD), a trademark for Microsoft's implementation of advanced interactivity for HD DVD
• Histone deacetylase inhibitor, compounds used in psychiatry and neurology, and with anticancer potential
• HDI-45 connector, a video connector by Apple
• Heroux-Devtek Inc., a manufacturer of aircraft undercarriages
• Help Desk Institute, a professional organization for those working in the IT Service Management industry.
• High Density Interconnects, technology for complex electronic circuit designs in small form factor
• Hdi, an Afro-Asiatic language

The PSA Group sells a variety of diesel automobile engines with the HDi (high-pressure direct injection) designation. Earlier versions were exclusive to Peugeot and Citroën. In 1998, PSA entered into a joint venture with the Ford Motor Company to produce a range of new diesel engines. The joint venture makes identical engines which are fitted to a variety of vehicles from a range of car manufacturers. The engines are assembled in production plants in the cities of Trémery and Douvrin for PSA in France, at the Ford Dagenham plant in the UK, and the Ford-owned Volvo Engine Plant in Skövde Sweden.