Background: Lack of alignment or harmony between information technology (IT) and business imperatives continues to plague organisations despite decades of research. Strategic information systems planning (SISP) is the process of coordinating the relationship between IT and the business in order to steer alignment. Shared domain knowledge (SDK) is a factor that is posited as important for improving both SISP and alignment, which is theorised to be the main outcome of SISP. Objectives: The aim of this article is to examine the impact of SDK on SISP and alignment. Method: Data were gathered from management consultants in a large, global IT organisation, through the use of a structured questionnaire, and analysed. Results: It was shown that SDK positively influences SISP characteristics and the alignment outcome. Specifically, it was found that high levels of rationality in SISP positively influenced the intellectual dimension of alignment, whilst IT manager participation in business planning influenced the social dimension of alignment. SDK was found to have a bearing on all of the SISP characteristics measured (i.e. rationality, adaptation, business planning-SISP integration and IT manager participation in business planning). SDK was also found to positively impact both the intellectual and social dimensions of alignment.Conclusion: The implications of the findings are that fostering a knowledge sharing environment in organisations will help improve alignment, as well as the formal processes designed to steer alignment such as SISP.