Period numbers form a countable subset of the complex numbers. One can describe periods via a pairing between (algebraic) de Rham cohomology and singular cohomology or using semi-algebraic sets. A variant are exponential periods which admit similar descriptions, where singular cohomology is replaced by rapid decay cohomology and semi-algebraic sets are replaced by sets definable in a certain o-minimal structure. This talk will be an introduction to these ideas.

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