42Axx | 40 | 42 | 42B |
| 42A05 | Trigonometric polynomials, inequalities, extremal problems |
| 42A10 | Trigonometric approximation |
| 42A15 | Trigonometric interpolation |
| 42A16 | Fourier coefficients, Fourier series of functions with special properties, special Fourier series {For automorphic theory, see mainly 11F30} |
| 42A20 | Convergence and absolute convergence of Fourier and trigonometric series |
| 42A24 | Summability and absolute summability of Fourier and trigonometric series |
| 42A32 | Trigonometric series of special types (positive coefficients, monotonic coefficients, etc.) |
| 42A38 | Fourier and Fourier-Stieltjes transforms and other transforms of Fourier type |
| 42A45 | Multipliers |
| 42A50 | Conjugate functions, conjugate series, singular integrals |
| 42A55 | Lacunary series of trigonometric and other functions; Riesz products |
| 42A61 | Probabilistic methods |
| 42A63 | Uniqueness of trigonometric expansions, uniqueness of Fourier expansions, Riemann theory, localization |
| 42A65 | Completeness of sets of functions |
| 42A70 | Trigonometric moment problems |
| 42A75 | Classical almost periodic functions, mean periodic functions [See also 43A60] |
| 42A82 | Positive definite functions |
| 42A85 | Convolution, factorization |
| 42A99 | None of the above, but in this section |