Strategic Information Systems Planning (SISP) is the process of aligning an organization's business strategy with effective computer-based information systems to achieve critical business objectives. SISP is a top concern of major executives and considerable resources (time and money) are spent in SISP activities. Many SISP initiatives are not successful due to the difficulty of implementing the recommendations. A significant problem is the Specification Gap between the description of the recommended systems and the detail needed for actual system implementation. Existing SISP methods do not provide sufficiently rigorous representations to specify detailed system recommendations. Box structures are proposed as a solution to this problem and a SISP process with embedded box structure methods is presented. We have used this innovative process in two SISP projects with large organizations. Partial results from one of the projects are presented as a case study to illustrate the use of box structures and their benefits