68Qxx Theory of computing
 68Q01 General
 68Q05 Models of computation (Turing machines, etc.) [See also 03D10, 68Q12, 81P68]

68Q10 Modes of computation (nondeterministic, parallel, interactive, probabilistic, etc.) [See also 68Q85]
(2)
 68Q12 Quantum algorithms and complexity [See also 68Q05, 81P68]

68Q15 Complexity classes (hierarchies, relations among complexity classes, etc.) [See also 03D15, 68Q17, 68Q19]
(2)

68Q17 Computational difficulty of problems (lower bounds, completeness, difficulty of approximation, etc.) [See also 68Q15]
(1)
 68Q19 Descriptive complexity and finite models [See also 03C13]

68Q25 Analysis of algorithms and problem complexity [See also 68W40]
(18)
 68Q30 Algorithmic information theory (Kolmogorov complexity, etc.) [See also 03D32]

68Q32 Computational learning theory [See also 68T05]
(1)
 68Q42 Grammars and rewriting systems
 68Q45 Formal languages and automata [See also 03D05, 68Q70, 94A45]
 68Q55 Semantics [See also 03B70, 06B35, 18C50]
 68Q60 Specification and verification (program logics, model checking, etc.) [See also 03B70]
 68Q65 Abstract data types; algebraic specification [See also 18C50]
 68Q70 Algebraic theory of languages and automata [See also 18B20, 20M35]
 68Q80 Cellular automata [See also 37B15]
 68Q85 Models and methods for concurrent and distributed computing (process algebras, bisimulation, transition nets, etc.)
 68Q87 Probability in computer science (algorithm analysis, random structures, phase transitions, etc.) [See also 68W20, 68W40]
 68Q99 None of the above, but in this section