Starting with a discussion of periodic functions, this exposition advances to the almost periodic case, an area of study that was suggested to author Harald Bohr by questions about which functions could be represented by a Dirichlet series. An appendix covers the almost periodic functions of a complex variable. Bohr's groundbreaking work influenced many later mathematicians who extended his theory in new and diverse directions. AUTHOR: Harald August Bohr (1887?1951) was a Danish mathematician, and the brother of Nobel Prize-winning physicist Niels Bohr. He worked primarily in the area of mathematical analysis and was the founder of the field of almost periodic functions.
