- Lidar
- Liebig condenser
- Life cycle thinking
- Life-cycle assessment
- Lift
- Lift-to-drag ratio
- Lifting gas
- Ligand-gated ion channels
- Ligands
- Light rail
- Light-dependent reactions
- Light-water reactor
- Lightfastness
- Lightning
- Lignin
- Lignite
- Limb
- Lime
- Lime mortar
- Lime plaster
- Lime render
- Lime softening
- Limescale
- Limestone
- Limewater
- Liming
- Limit state design
- Limiting oxygen concentration
- Limiting reagent
- Limnology
- Limonene
- Limonite
- Line-of-sight propagation
- Linear algebra
- Linear combination
- Linear combination of atomic orbitals
- Linear compressor
- Linear elasticity
- Linear independence
- Linear map
- Linear regression
- Linearity
- Linpack
- Linseed oil
- Lipids
- Lipophilicity
- Liposomes
- Liquefaction
- Liquefied gas
- Liquid air
- Liquid carbon dioxide
- Liquid crystals
- Liquid helium
- Liquid hydrogen
- Liquid junction potential
- Liquid metal
- Liquid metal cooled reactor
- Liquid metal embrittlement
- Liquid nitrogen
- Liquid oxygen
- Liquid-propellant rocket
- Liquid-ring pump
- Litharge
- Lithification
- Lithiophilite
- Lithium
- Lithium carbonate
- Lithium hydroxide
- Lithium iron phosphate battery
- Lithium nickel manganese cobalt oxide
- Lithium nitride
- Lithium oxide
- Lithium perchlorate
- Lithium peroxide
- Lithium polymer battery
- Lithium soap
- Lithium stearate
- Lithium-air battery
- Lithium-ion battery
- Lithosphere
- Litmus
- Litter
- Little Ice Age
- Liver
- Liver failure
- Living polymerization
- Living streets
- Load factor
- Load-bearing walls
- Loam
- Lobe pump
- Loci
- Locks
- Loess
- Log-normal distribution
- Logarithmic scale
- Logarithms
- Logic gates
- Logistics
- Lone pairs
- Long QT syndrome
- Long-lived fission products
- Long-term pavement performance
- Longerons
- Longitudinal waves
- Longwave
- Loop diuretics
- Lorentz force
- Loss on ignition
- Lost-wax casting
- Lotus effect
- Loudspeaker
- Louvers
- Low back pain
- Low-cycle fatigue
- Low-pressure area
- Low-temperature distillation
- Lower respiratory tract infections
- Lubricants
- Lubrication
- Lubricity
- Luminescence
- Luminescent solar concentrator
- Luminosity
- Lung
- Lung volumes
- Lupus
- Lustre
- Lutetium
- Lux
- Lye
- Lymph
- Lymphatic vessels
- Lysine
- Lysis
- MBE
- MEKP
- MEO
- MER
- MESFET
- METAR
- MOSFETs
- MOX fuel
- MPI
- MRE
- MRI
- MRI contrast agent
- MRI sequences
- MSR
- MTBF