There are a number of well documented fundamental assumptions associated with strategic information systems planning (SISP). A core activity for this domain is the alignment of an organisations systems and technology strategy with its business objectives. The difficulty is the complex and diverse nature of the strategy process itself which renders such a match increasingly problematic. The evidence within the literature relating to SISP suggests that it does not fully mirror contemporary business strategy and contains some fundamentally incorrect assumptions. This paper identifies eight such assumptions which propose a number of challenges for future research directions. Finally, a number of challenges to SISP are noted which relate to identified categories, through an IS complexity framework for sustainable competitive advantage.