- Kaplan turbines
- Karst springs
- Kelvin equation
- Kelvin probe force microscope
- Kenyaite
- Keratin
- Keratinocytes
- Kerogen
- Ketones
- Ketoprofen
- Kevlar
- Kidney
- Kidney dialysis
- Kidney disease
- Kidney failure
- Kiln
- Kiln furniture
- Kilogram
- Kilopower
- Kilowatt-hour
- Kimberlite
- Kinetic energy
- Kinetic energy penetrator
- Kinetic isotope effect
- Kinetic theory of gases
- Kites
- Kjeldahl method
- Knitting
- Knudsen cell
- Knudsen number
- Kondo effect
- Kondo insulators
- Kraft paper
- Kroll process
- Krypton
- LAH
- LBE
- LC
- LCD
- LCST
- LEED
- LEIS
- LEO
- LES
- LFTR
- LMIS
- LNG
- LTE
- Laboratory flasks
- Laboratory glassware
- Lacquer
- Lactic acid
- Lactobionic acid
- Lagoon
- Lakes
- Lamb shift
- Lambert's cosine law
- Lamellar structure
- Laminar flow
- Laminated glass
- Lamination
- Land footprint
- Land rehabilitation
- Landfill gas
- Landfills
- Landing
- Landing gear
- Landline
- Landscape
- Landscaping
- Landslide dam
- Lane departure warning system
- Langbeinite
- Lanthanide contraction
- Lanthanides
- Lanthanum
- Lanthanum oxide
- Laplace pressure
- Lapping
- Lapse rate
- Laptop
- Large intestine
- Larmor precession
- Larnite
- Laser
- Laser beam welding
- Laser cooling
- Laser cutting
- Laser diodes
- Laser dye
- Laser engraving
- Laser linewidth
- Laser peening
- Latent heat
- Laterite
- Latex
- Lath
- Lath and plaster
- Lathe
- Latitude
- Lattice constant
- Lattice energy
- Launch vehicles
- Lauric acid
- Lava
- Laves phases
- Law of thermodynamics
- Lay-up process
- Layered materials
- Le Chatelier's principle
- Leachate
- Lead abatement
- Lead carbonate
- Lead chloride
- Lead chromate
- Lead citrate
- Lead compounds
- Lead dioxide
- Lead glass
- Lead oxide
- Lead paint
- Lead poisoning
- Lead shielding
- Lead sulfate
- Lead sulfide
- Lead-acid battery
- Lead-cooled fast reactor
- Leading edges
- Leading-edge slats
- Leaf springs
- Leak detection
- Leap years
- Lebesgue measure
- Leblanc process
- Ledeburite
- Legendre transformation
- Leidenfrost effect
- Length contraction
- Lennard-Jones potential
- Lens
- Lepidocrocite
- Lepidolite
- Lethal dose
- Leucite
- Leucogranite
- Levees
- Level crossings
- Lever
- Lever rule
- Lichen