- Radiation pressure
- Radiation protection
- Radiation therapy
- Radiative cooling
- Radiative transfer
- Radical anion
- Radical initiator
- Radicals
- Radio
- Radio astronomy
- Radio broadcasting
- Radio navigation
- Radio noise
- Radio propagation
- Radio receivers
- Radio spectrum
- Radio waves
- Radioactive contamination
- Radioactive decay
- Radioactive tracers
- Radioactive waste
- Radiocarbon dating
- Radiology
- Radiometry
- Radionuclides
- Radiopharmaceuticals
- Radiopharmacology
- Radiosurgery
- Radium
- Radium sulfate
- Radius of curvature
- Radius of gyration
- Radomes
- Radon
- Rafters
- Rail transport
- Railway electrification
- Railway engineering
- Rainflow-counting algorithm
- Rainscreen
- Rainwater harvesting
- Raman laser
- Raman scattering
- Raman spectroscopy
- Ramjet
- Rammed earth
- Random coils
- Randomness
- Raney Nickel
- Rankine cycle
- Rankine scale
- Raoult's law
- Rapeseed oil
- Rapid prototyping
- Rare-earth elements
- Rare-earth magnet
- Rarefaction
- Raschig rings
- Rash
- Raster graphics
- Ratchets
- Raw materials
- Ray casting
- Ray tracing
- Rayleigh scattering
- Rayon
- Razor
- Reaction intermediates
- Reaction mechanism
- Reaction rate
- Reactive centrifugal force
- Reactive diluent
- Reactivity
- Reactivity series
- Reactor-grade plutonium
- Ready-mix concrete
- Reagents
- Real estate development
- Real number
- Realgar
- Rear-end collision
- Rebar
- Receiver
- Rechargeable battery
- Reciprocating engines
- Reciprocating pump
- Reclaimed water
- Recoil
- Reconstruction
- Recrystallization
- Rectangle
- Rectangular cuboid
- Rectifier
- Recycled wool
- Recycling
- Red blood cell
- Red mud
- Redistribution
- Redox
- Redshift
- Reducing agents
- Reducing atmosphere
- Redundancy
- Reefs
- Reference electrode
- Refinery
- Refining
- Reflectance
- Reflection
- Reflux
- Reforestation
- Refraction
- Refractive index
- Refractory
- Refractory metals
- Refrigerants
- Refrigeration
- Refrigerator
- Regenerative braking
- Regenerative cooling
- Regolith
- Regular icosahedron
- Regular polygon
- Reinforced carbon-carbon
- Reinforced concrete
- Reinforced concrete column
- Reinforcement
- Relative atomic mass
- Relative density
- Relative permittivity
- Relaxation
- Relays
- Release agents
- Reliability engineering
- Reluctance motor
- Remote sensing
- Renal colic
- Rendering
- Renewable energy
- Renewable resources
- Renin
- Renin-angiotensin system
- Rent-seeking
- Repairability
- Repeat unit
- Repeater
- Repointing
- Reprocessed uranium
- Reproducibility
- Reproductive system