In Chap. 9 Primas unpacks his technical repertoire on group theory and algebras of observables by introducing and employing temporal groups and algebras, their representations, and corresponding descriptions of temporal phenomena. Of major relevance for the notions of sequential and non-sequential time are the affine time group and the affine frequency group, which can be realized by time and frequency operators referring to past and future as well as positive and negative frequencies, respectively.