This dissertation is devoted to a perspective from which IT-based information systems are conceived as information technological artefacts intended for business action and communication. The perspective has been made concrete through the concept of information systems actability, which is the main concept under scrutiny. The research contributions of the dissertation exist at various levels of abstration. First of all, the dissertation contributes to the understanding of information systems from a social action perspective. Based on identified weaknesses in contemporary conceptualizations of information systems, the concept of information systems actability is developed. This contribution consists of a reconciliation of various views on information system usage quality with its roots in a linguistic tradition including elements from organizational semiotics and the language/action perspective. At a more concrete level, this understanding, and the concept as such, have consequences for the development and evaluation of information systems. Such consequences have been the foundation for a proposed information systems design method, which thus constitutes a further contribution. Another contribution is the outlining of an information systems actability. As a further means of obtaining empirical experience of working with this concept, a descriptive analytic framework has been developed, which constitutes yet another contribution. These three operationalizations, the design method, the evaluation method and the analytic framework, have been developed and empirically grounded through a qualitative case study appproach involving four cases of information systems requirements specification, four evaluations of existing information systems, and two cases of description and characterization of information systems related phenomena from the perspective of actability. The latter two cases imply how further contributions at an even more concrete level, constituted by characterizations of Internet-based information systems and the local electronic marketplace, seen in the light of information systems actability.