E-business might be characterized by open system through internet, fortification of relationship between the suppliers and customers in chain system of company, the collaboration among partners and the use of IT. For these characteristics, e-business companies are becoming to suffer such burdens as wide spread of global economy, industry deregulation, and the increasing number of new entrants. In this situation, e-business companies should maintain the flexible system to adapt fast changing environment. Information system planning has been the important research area for many years because of its strategic importance. Among various variables, organization and IS context have been researched for making successful ouput of ISP. In this paper, I studied the importance of flexibility in e-business environments. And further I examined the flexibility of IS, organization and ISP methodologies. The forthcoming paper, I expect to investigate the relationship between IS flexibility, organizational flexibility, ISP flexible methodologies and successful ISP.