| Acronym | Meaning |
| GWRTAC | Groundwater Remediation Technologies Analysis Center |
| GWSS | Groundwater Supply Survey |
| GWTR | Ground Water Treatment Rule |
| GX | Generalized Exchange |
| H-CI | Hylleraas-configuration Interaction |
| H-FABP | Heart Fatty Acid-binding Protein |
| HAA | Haloacetic Acid |
| HAA | Heterocyclic Aromatic Amine |
| HAADF | High-angle Annular Dark-field |
| HAART | Highly Active Antiretroviral Therapy |
| HAB | Harmful Algal Bloom |
| HAB | High-Alumina Basalt |
| HABR | Hybrid Anaerobic Baffled Reactor (for Wastewater Treatment) |
| HAC | High Alumina Cement |
| HAC | Hydrogen-assisted Cracking |
| HACCP | Pathogen Reduction And Hazard Analysis Critical Control Point |
| HACS | Hazard Assessment Computer System |
| HAD | High Aluminum Defect |
| HAD | Hollow Anode Discharge |
| HADD | Highest Average Daily Dose |
| HADES | High Activity Disposal Exptl. Site [for Radioactive Waste] |
| HADS | Health Assessment Documents |
| HAEC | Human Aortic Endothelial Cell |
| HAEC | Human Artificial Episomal Chromosome |
| HAF | Halogen Acid Furnaces (for Burning Halogenated Wastes |
| HAFID | Hydrogen Atmosphere Flame Ionization Detector |
| HAGAR | High Altitude Gas Analyzer |
| HAGIS | Headspace Analysis Gas-phase Infrared Spectroscopy |
| HAI | Histol. Activity Index |
| HAISP | High Altitude Interactive Science Platform |
| HAL | Health Advisory Level |
| HALOE | Halogen Occultation Experiment |
| HALS | Hindered-amine Light Stabilizers |
| HALT | Hydrate Addition At Low Temperature (for Sulfur Dioxide Removal From Flue Gases) |
| HAM | Hydrogenic Atoms In Molecules |
| HAM/N | Hydrogenic Atoms In Molecules |
| HAMA | Human Anti-mouse Antibody |
| HAMR | Heat Assisted Magnetic Recording |
| HAMS | Helium Atoms Measurement System |
| HAN | Halogenated Acetonitrile(s) |
| HAN | Heavy Aromatic Naphtha |
| HAN | Hydroxylamine Nitrate (salt) |
| HANS | Heavy Aromatic Naphtha Solvent |
| HAO | Hybrid Atomic Orbital |
| HAO | Hydrogenic Atomic Orbital |
| HAOM | Hybrid Atomic Orbital Model |
| HAP | Hazardous Air Pollutants |
| HAPEM | Hazardous Air Pollutant Exposure Model |
| HAPEMS | Hazardous Air Pollutant Enforcement Management System |
| HAPEX | Hydrological And Atmospheric Pilot Experiment |