| Abbreviation | Definition |
|---|---|
| HOTA | HUMINT Operational Tasking Authority |
| HPA | Hamburg Port Authority |
| HRDA | Human Resources Development Authority |
| HSHA | High Security Hospital Authority |
| HSWA | Hampton Shaler Water Authority |
| HTA | Human Tissue Authority |
| HTA | Humboldt Transit Authority |
| HTWA | Huston Township Water Authority |
| HWHA | Haudenosaunee Wildlife and Habitat Authority |
| HWHA | Haudenosaunee Wildlife Habitat Authority |
| IAA | Indianapolis Airport Authority |
| IAA | Installation Assurance Authority |
| IAA | Israel Airports Authority |
| IAA | Israel Antiquities Authority |
| IAC | Issuing Authority Code |
| IAGA | Indian Artifact Grading Authority |
| IANA | Internal Associative Numbers Authority |
| IANA | Internet Assigned Names Authority |
| IANA | Internet Assigned Node Authority |
| IATT | Interim Authority to Test |