Strategic information systems planning (SISP) remains a primary concern for many organisations. It is reportedly a top concern of not only the Information Systems (IS) executives but also of many chief executives. Recently, calls have been madefor better understanding of strategic planning in general, including SISP, and especially for studies of actual planning behaviour in organisations. As doubts continue to be raised about the payoff ofIT, it is important to examine the effectiveness ofmany accepted IS management practices such as SISP. Accordingly, researchers have investigated SISP practice and proposed both formal methods and principles of good practice. SISP cannot, however, be understood by considering formal methods alone. Yhe processes of planning and the implementation of plans are equally important However, there have been very few investigations of these phenomena. More surprisingly, few studies have been undertaken to identify and understand: (]) the approaches to SISP adopted in practice, (2) the relationship between SISP approaches and its ultimate success, (3) the influence of organisational and technological context on planning success. Yhis study helps to fill this vacuum in the important research area. A formal survey of IS Directors, which generated two hundred and ninety two, responses was initiated to empirically investigate these issues. The categorisation of SISP approaches adopted by companies was accomplished by performing cluster analysis, based on chosen IS planning dimensions, namely., comprehensiveness, participation, formalisation, flow, focus, frequency, alignment, ownership, IS benefit and plan implementation. Using this multivariate technique, four unique and stable groups were identified, namely: (1) organisational, (2) business-led, (3) administrative and (4) formal, This derived taxonomy was thoroughly validated to ensure that it is exhaustive, mutually exclusive, stable and consistent. Within this study,S ISPs uccessh as been conceptualisedb asedo n the extento f thefollowing measures: (1) alignment, (2) analysis, (3) co-operation, (4) implementation, (5) capabilities,( 6) satisfactiona nd (7) contribution. Thes tudyh as also conceptualisedS ISP success in terms of an aggregate score. It is found that each approach, with its different characteristics, has a different likelihood of success. Thefindings of this research suggest that the Organisational approach, which is characterised by high levels of alignment, comprehensivenespsa, rticipation,f requency,i nfusion benefita ndp lan implementationi,s by far the most successful. Conversely, the Administrative approach which has low levels of comprehensivenessfr, equency, participation and alignment is the least successful. Interestingly,t his study also suggeststh at the Organisationala pproach deliversa high level ofSISP successir respectiveo fthe organisationala nd technologicalc ontexto f the company. In summary, this study has extended our understanding of SISP processes and has provided useful insightsfor IS executives and top management in general, in implementing SISP within their organisations.