- Infrared detectors
- Infrared lamp
- Infrared spectroscopy
- Infrastructure
- Infrastructure asset management
- Ingestion
- Ingot
- Inhalants
- Inhalation
- Injection moulding
- Inkjet printing
- Inland seas
- Inlays
- Inner product space
- Innovation
- Inorganic chemistry
- Inorganic compounds
- Inorganic polymers
- Input impedance
- Insect flight
- Inspection
- Insulated glazing
- Insulating Concrete Form
- Insulators
- Intake
- Integers
- Integrated design
- Integrated passive devices
- Integrating sphere
- Interatomic potentials
- Intercalation
- Intercooler
- Interfacial thermal resistance
- Interference fit
- Intergranular fracture
- Interleukins
- Interlocking
- Intermediate composition
- Intermetallic
- Internal energy
- Internal fixation
- Internal pressure
- Internal rate of return
- Internal standard
- International System of Units
- International temperature scale of 1990
- Internet
- Internet Protocol Suite
- Interstitial site
- Interventional radiology
- Intraclasts
- Intrinsic semiconductor
- Introduced species
- Intrusive rock
- Intumescent
- Invar
- Inversion temperature
- Inversions
- Invertible matrix
- Investment casting
- IoT
- Iodine-131
- Ion association
- Ion beam
- Ion channels
- Ion exchange
- Ion implantation
- Ion laser
- Ion pumps
- Ion transporter
- Ion trap
- Ion-exchange membranes
- Ion-exchange resin
- Ion-selective electrode
- Ionic compounds
- Ionic conductivity
- Ionic crystal
- Ionic liquids
- Ionic radius
- Ionic strength
- Ionization
- Ionization energy
- Ionizing radiation
- Ionomers
- Ionophores
- Ionosphere
- Iridescence
- Iridium
- Iron
- Iron chloride
- Iron compounds
- Iron cycle
- Iron group
- Iron hydroxide
- Iron ore
- Iron overload
- Iron oxide
- Iron oxide cycle
- Iron oxide nanoparticles
- Iron pentacarbonyl
- Iron-deficiency anemia
- Ironstone
- Irradiance
- Irrigation
- Irritation
- Isasmelt
- Isentropic process
- Isobaric process
- Isobars
- Isobutyraldehyde
- Isochoric process
- Isocyanate
- Isocyanide
- Isomerases
- Isomerization
- Isomers
- Isopentane
- Isoperimetric inequality
- Isopropyl alcohol
- Isothermal process
- Isotope fractionation
- Isotope separation
- Isotopes
- Isotopic labeling
- Isozymes
- Iterative reconstruction
- Izod impact strength test
- J-integral
- JFET
- JP-4
- JP-8
- James Parker
- Jerk
- Jet Age
- Jet aircraft
- Jet engine
- Jet fuel
- Jetty
- Johnson-Nyquist noise
- Joint
- Joint replacement
- Joists
- Joule heating
- Jumpers
- Junction temperature
- Jute
- Juvenile idiopathic arthritis
- Kankar
- Kanthal
- Kaolinite