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...