Abstract: In recent years climate change and other urban growth considerations have put sustainable urban development at the forefront of most strategic policy discussions in almost every city across the world, including Australia (Commonwealth of Australia, 2011). The increased and urgent environmental agenda has engendered the need for employing sustainability assessment frameworks as key mechanisms to guide urban planning and policy development. Urban systems emerge as distinct entities from the complex interactions among three interconnecting and overlapping primary systems: the environment, the economy and society. Such complexity poses a challenge to identify the causes of urban environmental problems and how to address them without causing greater deterioration. Urban planning has traditionally addressed these problems with policies regulating the location and intensity of urban activities, often based on assumptions about urban and environmental dynamics that are rarely revisited (Alberti, 1999; Neuman, 2005). Given the complexity of urban systems and the environment that supports them, the key intellectual challenge of urban sustainability is an improved understanding of the dynamic spatial relationships and interactions among different urban and environmental systems. Such an understanding can inform policy and decision making of the consequences and challenges faced when responding to urban needs. We seek to contribute to this understanding by developing a multi-dimensional assessment framework. The assessment framework consists of normative guiding concepts on how the concept of sustainable development can be applied (the normative dimension), a target system to be assessed (the systemic dimension), an appropriate procedure to integrate the relevant stakeholders and to bridge the normative and systemic aspects (the procedural dimension) and the use and integration of modelling activities (the supportive dimension). In this paper we focus on the role and use of modelling activities in urban planning and policy development in general. The focus here is on "applied" models, i.e. models which try to simulate real-world processes based on or calibrated to empirical information. Detailed information on specific models, their strengths, weaknesses and major applications are not included in this paper. The sustainability literature has acknowledged that new methods and tools are needed to support an improved understanding of the dynamics and interrelationships between social, economic and ecological systems (Weaver and Rotmans, 2006; Weaver and Jordan, 2008). However, despite significant progress towards the development of computer models to support policy formulation, their use is far away from being trivial or the norm. From literature (Lee, 1973, 1994; Brugnach et.al., 2007; Harding, 2007; Waddell, 2010) and interviews with key local government officers, we find that there are common challenges to appropriating a modelling system in government. Officers' limited understanding of urban modelling and a lack of system thinking skills are some of the challenges that need to be addressed before they can take advantage. The paper explores these modelling challenges, using them to inform the development of a set of modelling imperatives that supports the implementation of an improved assessment framework. Views from respondents indicate that implementation of these imperatives is likely to improve the level of confidence of officers to use models to support policy development and assessment practices. The paper concludes with a roadmap, briefly outlining the testing and evaluation of the framework as part of a case study implementation in Logan City.