China 
Africa 
- Columnar jointing
- Columns
- Com ports
- Coma
- Coma scale
- Comamonas testosteroni
- Comb drive
- Comb filter
- Comb generator
- Combi aircraft
- Combination drugs
- Combination reaction
- Combination therapy
- Combinational logic
- Combinatorial chemistry
- Combinatorial design
- Combinatorial explosion
- Combinatorial game theory
- Combinatorial optimization
- Combinatorics
- Combined cycle
- Combined cycle power plant
- Combined forced and natural convection
- Combined gas and steam
- Combined sewer
- Combined transport
- Combretastatin a-4
- Combustion
- Combustion analysis
- Combustion chamber
- Combustion instability
- Combustor
- Comet assay
- Cometabolism
- Comets
- Command
- Command language
- Command queue
- Comments
- Commercial waste
- Commercialization
- Commercialization of the internet
- Comminution
- Commissioning
- Commissures
- Commit
- Committed step
- Committee
- Committee machines
- Commodity hardware
- Commodity plastics
- Commodore PET
- Common Lisp
- Common Open Policy Service
- Common base
- Common bile duct
- Common carotid artery
- Common cold
- Common collector
- Common data model
- Common drain
- Common emitter
- Common gate
- Common hepatic artery
- Common hepatic duct
- Common iliac arteries
- Common iliac artery
- Common industrial protocol
- Common rail
- Common source
- Common subexpression elimination
- Common-ion effect
- Common-method variance
- Common-mode rejection ratio
- Common-mode signal
- Common-path interferometer
- Commonsense knowledge
- Commotio cordis
- Communication channels
- Communication complexity
- Communication design
- Communication protocols
- Communication software
- Communication source
- Communication system
- Communications satellites
- Communications security
- Community cloud
- Community design
- Community fingerprinting
- Community informatics
- Community solar
- Community-acquired pneumonia
- Commutation
- Commutative algebra
- Commutative property
- Commutative rings
- Commutator
- Commutator subgroup
- Commute
- Comonomer
- Comorbidity
- Compact
- Compact operators
- Compact-open topology
- CompactRIO
- Compacted graphite iron
- Compaction
- Compaction simulation
- Compactness measure
- Compactors
- Companding
- Companion diagnostics
- Companion robot
- Comparability
- Comparable
- Comparative Toxicogenomics Database
- Comparative genomics
- Comparative physiology
- Comparator
- Compartment syndrome
- Compartmentalisation
- Compartments
- Compass and straightedge
- Compasses
- Compatibility
- Compatibilization
- Compendium
- Compensatory growth
- Competence
- Competent
- Competitive inhibition
- Competitive inhibitor
- Competitive learning
- Competitor analysis
- Compile time
- Compiler
- Compiler optimization
- Complement
- Complement receptor 1
- Complement system
- Complement-dependent cytotoxicity
- Complementarity
- Complementarity-determining region
- Complementary
- Complementary events
- Complementary goods
- Complementation
- Complemented
- Complemented lattice