Experience sampling is considered one of the best methods for measuring behavior (Furr, 2009, https://doi.org/10.1002/per.724). When used for this purpose, it requires a coding system to transform diversified reports on what people are doing, provided as responses to an open-ended question, into interpretable data. We present a categorization of everyday behaviors that can be used to code responses from experience sampling and diary studies conducted with different groups of participants—from adolescents to elderly people. This categorization was developed and validated on a set of 19,840 responses to an open-ended question about participants’ recent activity, provided by 667 persons ranging in age from 12 to 66. As a result of the multistage work, we present a categorization system which forms a hierarchy from three broad categories to 97 narrow ones through middle levels of five, 23, and 63 categories of behaviors. The possible usage of the developed categorization is discussed.