- Atomic number
- Atomic orbitals
- Atomic radius
- Atomic ratio
- Atomic spacing
- Atrial fibrillation
- Attenuation
- Attenuation coefficient
- Atterberg limits
- Attrition
- Audits
- Auricupride
- Aurora
- Austempering
- Austenite
- Austenitic stainless steel
- Autism spectrum
- Autocatalysis
- Autoclaved aerated concrete
- Autogenous welding
- Autoignition temperature
- Automata
- Automated fiber placement
- Automatic transmission
- Automatic transmission fluid
- Autopilot
- Autopsy
- Autoregulation
- Autorotation
- Autoxidation
- Avalanche breakdown
- Avenues
- Avgas
- Aviation safety
- Axial ratio
- Axial symmetry
- Axial-flow pump
- Axiom
- Axle
- Azeotropic
- Azide
- Azo compounds
- Azo dyes
- Azurite
- BEM
- BET theory
- BEV
- BJT
- BLEVE
- BMC
- BOD
- BREEAM
- BREST
- BTL
- BTU
- BTX
- BWR
- Babbitt
- Back pressure
- Backhoe
- Backward compatibility
- Bacteria
- Bainite
- Bake-out
- Ball bearings
- Ball mill
- Ballast
- Ballistic conduction
- Ballistics
- Balloons
- Band gap
- Banded iron formation
- Bandwidth
- Bank
- Bar stock
- Barbecue
- Barges
- Barium
- Barium chloride
- Barium nitrate
- Barium sulfate
- Barium titanate
- Barometers
- Baryte
- Basal lamina
- Basalt
- Basalt fiber
- Base course
- Base load
- Base metals
- Base oil
- Base pairs
- Basement
- Basic oxygen steelmaking
- Bassanite
- Batch production
- Batholiths
- Bathymetry
- Baud
- Bauxite
- Bayer process
- Beach
- Beach nourishment
- Beam and block
- Bearing capacity
- Bearings
- Beaufort Scale
- Becquerel
- Bedrock
- Beds
- Belite
- Belleville washer
- Bellows
- Belt
- Benchmark
- Bending
- Bending machine
- Bending moment
- Bending of plates
- Bending stiffness
- Bentonite
- Benzaldehyde
- Benzalkonium chloride
- Benzene
- Benzoic acid
- Benzophenone
- Benzotriazole
- Benzoyl peroxide
- Bernoulli's principle
- Beryl
- Beryllium
- Beryllium copper
- Beryllium fluoride
- Beryllium oxide
- Bessemer process
- Beta decay
- Beta particles
- Beta-alumina solid electrolyte
- Betaine
- Betz's Law
- Bevel gears
- Bicarbonate
- Bicycle-friendly
- Bike lanes
- Bile duct
- Biliary tract
- Bimetallic strip
- Binary cycle
- Binary number
- Binary phase