- Hydrometallurgy
- Hydron
- Hydronium
- Hydrophile
- Hydrophobic
- Hydrophobic effect
- Hydrophobic silica
- Hydropneumatic suspension
- Hydropower
- Hydrosphere
- Hydrostatic
- Hydrostatic equilibrium
- Hydrostatic head
- Hydrotalcite
- Hydrothermal circulation
- Hydrothermal synthesis
- Hydrothermal vents
- Hydroxides
- Hydroxy group
- Hydroxyapatite
- Hydroxyl radicals
- Hydroxylamine
- Hydroxylation
- Hydrozincite
- Hygrometer
- Hypalon
- Hyperacusis
- Hyperbolic functions
- Hypercholesterolemia
- Hyperfine structure
- Hypergolic propellant
- Hyperkalemia
- Hyperloop
- Hypernatremia
- Hyperoxia
- Hyperphosphatemia
- Hyperpolarization
- Hypertension
- Hyperthermia
- Hypervelocity
- Hyperventilation
- Hypochlorite
- Hypokalemia
- Hyponatremia
- Hypotension
- Hypothermia
- Hypoventilation
- Hypovolemia
- Hypoxia
- Hysteresis
- I-beams
- I-type granite
- IBC
- IBM Blue Gene
- IC
- ICP
- IECC
- IFMIF
- IFR
- ILI
- IRMS
- ISA
- ISO metric screw thread
- ITO
- Ibuprofen
- Ice
- Ice caps
- Ice cores
- Ice crystal
- Ice sheets
- Iceland spar
- Icephobicity
- Icosahedra
- Ideal gas
- Ideal gas law
- Ideal solution
- Igneous intrusion
- Igneous rocks
- Ignition system
- Ignitron
- Ileus
- Illite
- Illuminance
- Ilmenite
- Image editing
- Image-guided surgery
- Imbibition
- Imides
- Imines
- Immune system
- Impact craters
- Impact extrusion
- Impeller
- Implants
- Impulse
- Impulse noise
- In silico
- In situ leach
- Incandescent light bulb
- Inch of mercury
- Inches
- Incineration
- Inclined plane
- Inclusions
- Incoloy
- Incompatible elements
- Inconel
- Indentation hardness
- Independent sideband
- Index ellipsoid
- Index finger
- Indigestion
- Indigo dye
- Indium
- Indium antimonide
- Indium gallium arsenide
- Indium gallium nitride
- Indium gallium phosphide
- Indium oxide
- Indium phosphide
- Indium-111
- Indole-3-acetic acid
- Indometacin
- Indoor air quality
- Induced demand
- Induction furnace
- Induction heating
- Inductive effect
- Inductively coupled plasma atomic emission spectroscopy
- Inductively coupled plasma mass spectrometry
- Industrial computed tomography
- Industrial engineering
- Industrial fermentation
- Industrial furnaces
- Industrial gas
- Industrial radiography
- Industrial waste
- Industrial wastewater treatment
- Inert gases
- Inertial frame of reference
- Inexact differentials
- Infections
- Infiltration
- Inflammasome
- Inflammation
- Inflammatory cytokines
- Inflatable
- Influence line
- Information age
- Infrared