This volume contains the invited paper, the reviewed research papers, the discussants' comments on the latter, and the workshop memoranda of the fourth IFIP WG 8. 1 International Working Conference on "Information System Concepts", with the subtitle "An Integrated Discipline Emerging" (ISC04). It was held in Leiden, The Netherlands, 20-22 September 1999. The previous three ISCO conferences were subtitled "An In-depth Analysis", "Improving the Understanding", and "Towards a Consolidation of Views". Their proceedings were published in 1989, 1992, and 1995, respectively. The ISCO conferences were instigated by the former Task Group FRISCO (an acronym for "FRamework of Information System Concepts"), charged by the IFIP Working Group 8. 1 with the task of proposing a conceptual framework for the information system field. Its report, entitled "A Framework of Information System Concepts" (the "FRISCO Report" for short), is available on the World Wide Web via the address: http://www. wi. leidenuniv. nl/~verrynstlfrisco. html or may be downloaded directly as a condensed Word-6 file from: ftp://ftp. leidenuniv. nl/pub/rullfri-full. zip The FRISCO Report forms a significant contribution to the long-lasting quest of our community towards developing a scientific outlook on the field of information systems. Clarifying the varied nature of many diverging views - some of which may not easily be reconciled - the report does propose a coherent, consistent and partially formalised framework of concepts.