This paper describes a five-stage Strategic Information Systems Planning (SISP) maturity model and a model for assessment of SISP in organisations based on the ‘Integral SISP Engineering’ approach and a unique implementation of the Analytical Network Process theory (ANP). The lack of SISP maturity definition is evident, and the literature has no segregation between SISP maturity and IS/IT departmental maturity. The SISP assessment model can be used as an early warning diagnostic tool to draw attention to particular aspects of the SISP that need improvement. The models are used to determine the degree of SISP maturity in Australian organisations.