In recent years the concept of mixed-use has emerged as a popular planning tool for urban planners to develop sustainable urban areas. With reason, because a clear positive relationship between function mix and urban sustainability in social, environmental and economic sense can be established from research. In practice however, we see that the physical interpretation of the concept of mixed-use and the urban area development process employed for mixed-use areas, although pursued enthusiastically in projects all over the world, varies greatly from project to project. The effect is that some (re) developed areas are not achieving the full sustainability benefits they aimed at with implementing mixed-use. A problem in practice is indicated that there is uncertainty in the field of urban area development on how to develop sustainable mixed-use urban areas, both in terms of product (what to develop) and process (how to develop it). This is subscribed by, although extensive research is done on both topics, a lack of formulated physical specifics in literature on the sustainable urban form of mixed-use, as well as lack of a clear answer on what development approach is best for developing mixed-use areas from the perspective of sustainabilty of the end-result. To enhance the success of this kind of developments, this paper will formulate a clear answer on the main research question ‘how can long term urban sustainability be achieved in urban area developments’ by determining the product (urban form) and process (development approach)- aspects that are important in the context of achieving sustainable mixed-use urban areas. This will be done by synthesizing the existing, dispersed knowledge on sustainable urbanism and urban area development along a well-substantiated perspective of ‘optimal’ sustainability and by studying two development approaches in practice. From this, a cohesive framework of aligned recommendations on urban form and development approach focused on achieving sustainable mixed-use areas will be made, providing actors in the urban area development process with the possibility to actively steer on these aspects and ensure better sustainable performances of the development result. Based on the findings from theory and empiry, the urban form that offers most potential for achieving long term urban sustainability in urban area developments can be defined as mixed-use neighbourhoods with specific physical features that foster walkability, vibrancy, diversity, freedom for the end-user to shape his own environment, and a sense of identity. Each of these features are substantiated by multiple researches. The concept of mixed-use development is appointed by practice as well as theory as the urban form that offers most potential of achieving long term urban sustainability. Long term urban sustainability is in this research defined as holistic long term economical, environmental and social viability of urban areas. Thorough reflection on the topic by contemporary theories on sustainable urbanism as well as long term successful examples from practice indicate that a high level of function mix is a critical component for urban sustainability, positively impacting urban sustainability in the social field and in the fields of transport, environment, and economy. The ‘optimal’ features from the perspective of long term urban sustainability have been defined as the features that achieve the most sustainable long-term end-user behaviour, since for endurance and viability it is essential for sustainable systems to be utilized and therefore to undertow a sustainable behaviour that will continue to exist. It overarches the different aspects of sustainability and brings them back to their initial driver. To do this, first the maximum sustainable benefits of mixed-use are translated into concrete goals for mixed-use. Theory on mixed-use offers solutions through which mixed-use development can achieve these goals. These solutions all presuppose a certain end-user behaviour. Finally, these end-user behaviours pose certain requirements to the urban form to induce and support this end-user behaviour, which are determined with the help of recommendations from literature, observation of practice and input of experts in the form of relevant physical variables. The exact physical characteristics of the urban form that are significant for the degree of urban sustainability of the area have been summarized in a list of variables, which are supplemented with their desired values from the perspective of urban sustainability. This list can serve as a guideline for achieving sustainability when designing mixed-use urban areas, by using it during the development process to oversee the impact on urban sustainability of proposed interventions and guard sustainable decision-making. To answer the question on the process dimension of which development approach offers most potential for achieving urban sustainability in mixed-use areas, literature on the urban area development process and possible development approaches has been reviewed with sustainable product-aspect of the previous part in mind. Furthermore, the two extremes of the possible development approaches have been studied in detail in practice through case studies of a bottom-up and top-down development approach in the Netherlands, giving a clear insight in the difficulties and threats to sustainability in the development process in practice, verifying and assessing recommendations from theory, and leading to specific recommendations from practice. The development approach determined as offering the most potential for achieving long term urban sustainability in the development result, is a combination of top-down and bottom-up planning in which the municipality sets out and guards a broad strategic course, focused on sustainability, and the developed is led by private parties (including housing associations) who develop the area in plots on own initiative according to their own ideas. In this development approach, private parties should be encouraged to take on responsibilities that go beyond the scale and term of the development of a single building, leading to larger scopes and longer term commitments and engagement in the development of the area as a whole. Plan development in this field is formed through participatory and collaborative decision-making processes in a setting of horizontal inter- actor relationships, in which the actors combine their means and knowledge to come to mutually beneficial, integrated solutions. End-users of the area should get a large influence over the shaping of their own environment, both through close inclusion in the development process or provided opportunities to build their own homes or business spaces through (collective) private commissioning formulas. The role of the public authorities and ultimately the municipality is to facilitate these private development initiatives, while at the same time keeping a strong direction over the process from a long term, wide-scope, public interest-oriented strategic planning basis. For this, an appropriate institutional framework has to be employed that finds a balance between the regulations necessary for the protection of the aims of the development and the qualities of the area, and a maximum degree of freedom for the development of valuable private initiatives. Finally, all of this should happen with a focus of long term urban sustainability in mind. This should be incorporated in the strategic plan and steering of the municipality, but should also be instated in the minds of the private actors participating in the urban area development, and guarded throughout the development process. Development of knowledge on the topic, corresponding actor education and employment of a pragmatic, and a sustainability-oriented working method that provides handles for the inclusion, operationalisation, guarding and monitoring of sustainable principles in the development process, all explained in the recommendations section of this research, should secure the integral consideration of this sustainable dimension in the urban area development process.