Strategic Information Systems Planning (SISP) is an important activity for helping Chief Information Executives (CIOs) and top management identify strategic applications and align Information Technology (IT) with business needs. Like all strategic planning, SISP requires measuring how well SISP is done and how planning is improving over time. The measurement of these intangibles is a complex exercise. There have been few efforts undertaken in the Information Systems (IS) literature to formally develop a model for assessing and measuring SISP efforts. In this study, two models were proposed: a five-stage SISP maturity model for defining SISP maturity and another one for assessing the degree of SISP maturity. The five SISP maturity levels were defined as: Rudimentary Planning, Ineffectual Planning, Attainable Planning, Sustainable Planning, and Adaptable Planning. The assessment model was structured as a third-order system, where eight first-order dimensions were termed as Form and Content, Collaboration, Policies, Stakeholders' Designation, Knowledge Bank, Technology, Time Dimension, and Viability. The first-order dimensions were grouped into three second-order constructs, namely Effectiveness, Efficiency and Manoeuvrability, which ultimately characterise the level of SISP success. This model was used to establish a theoretical benchmark for each SISP maturity level. To model the level of SISP maturity, an 'Integral Engineering' approach was established and the Analytic Network Process (ANP) theory was used. The study is a novel approach in using ANP to synthesize the measures of the various SISP constructs into a single overall measure of SISP maturity level. A survey was performed and data collected from 260 Australian organisations to examine the degree of SISP maturity and the relationships among SISP constructs. Structural equation modelling (SEM) was used to test the fit between the hypothesized model and the survey data The models were applied to the data collected and the findings suggested that the models fit the data well. While Effectiveness and Efficiency are well recognised planning constructs, Manoeuvrability as a measure of planning dynamics is not acknowledged in the literature as an equally important construct. This study confirmed a strong correlation between Manoeuvrability and SISP success and found it to be more important than the Efficiency construct. The empirical data did not confirm the existence of Rudimentary and Ineffectual planning levels of SISP maturity Australia-wide. SISP maturity in the majority of Australian organisations is at Sustainable and Attainable planning levels. A small percentage of the surveyed organisations have actually reached the highest planning level (Adaptable planning). The empirical data showed that current SISP is lacking strategic dimension and that the recently popularised one-year planning horizon may not be the best choice. Australian organisations did not consider the strategic relevance of IT as the key objective. IT/IS was seen as a business enabler, thus the strategic advan tage associated with IT came as a secondary objective.