Resumen
This review examines some particular, but important and basic aspects of information: Information is related to questions and should provide at least partial answers. Information comes in pieces, and it should be possible to aggregate these pieces. Finally, it should be possible to extract that part of a piece of information which relates to a given question. Modeling these concepts leads to an algebraic theory of information. This theory centers around two different but closely related types of information algebras, each containing operations for aggregation or combination of information and for extracting information relevant to a given question. Generic constructions of instances of such algebras are presented. In particular, the close connection of information algebras to logic and domain theory will be exhibited.