The Master’s programme Industrial Ecology is jointly organised by Leiden University and Delft University of Technology. Over the last few years the general awareness concerning sustainability increased significantly. Also companies are making big efforts to make their processes and products more sustainable. One of the key concepts in this search to more sustainable processes is the concept of Sustainable Development which is often defined as development that 'meets the needs of the present without compromising the ability of future generations to meet their own needs'. A concept within Sustainable Development which is often used is the Triple Bottom Line, which indicates the three pillars of sustainability: people, planet and profit. Within companies Management Systems focussed on environmental or social aspects are used to manage sustainability topics. These Sustainability Frameworks are used to identify and manage topics related to the sustainable performance of companies. Three major concepts within the management of Sustainable Development are Corporate Social Responsibility, Environmental Management System and Environmental and Social Reporting. An overview of a large number of available sustainability frameworks, as well as their properties has been made. The Capability Maturity Model is a model which is used in a wide variety of industries to indicate the maturity of different capabilities for processes within an organization. Based on the outcomes of the model the organization can improve its processes to disciplined management processes. The main advantages of a Capability Maturity Model are increase of business success, increase of cost effectiveness, possibility to combine with other technologies such as ISO standards, used in wide-variety of industries, long life-span and a good reputation among government and research institutes. Within this research the concept of the Capability Maturity Model has been combined with insights from the field of Sustainable Development in order to improve business performance in a sustainable manner, the Sustainable Development Maturity Model. The following components have been identified as essential for building a new Capability Maturity Model: A number of levels, General descriptor of each level, Generic description of the contents and characteristics of each capability level, A number of Key Performance Areas or dimensions, A number of topics and activities for each Key Performance Area, A description of each activity as it might be executed or performed at each maturity level. Six levels for the Sustainable Development Maturity Model have been defined based on existing definitions in other Capability Maturity Models and insights from the field of Sustainable Development. Level 0 indicates compliance to regulation and is a bottom-line requirement. For level 1 to level 5 generic definitions for the levels have been made containing contents and characteristics of the level as well as a generic descriptor for the levels. These descriptors are respectively: Initial, Initial Transformation, Light Sustainability, Sustainable Transformation and Reinforced Sustainability. A scoring system has been developed to indicate the correlation between the different layers of the system. The score of the different topics can be filled in at layer 5. The lowest score of the topics results in the score for the activity. The average score for the activity result in the score for the Key Sustainability Areas, unless there is a score 0, then it will result in a score 0. The lowest score for the Key Sustainability Areas result in the score for the framework (or the condition). The sensitivity of the scoring, which means the influence of a certain score on the end-result, has been tested using several cases. The information on the above mentioned frameworks have been expanded with information from its websites and quantitative information from websites as www.springerlink.com. From this list of frameworks three different frameworks have been selected for use in the Sustainable Development Maturity Model, one for every main category of conditions (Worker, Social and Environmental). By using knock-out criteria the number of frameworks was reduced to 8 (ISO 14001, ISO 26000, EMAS, OHSAS 18001, SA8000, AA1000, the Natural Step and Global Reporting Initiative). By looking to the background of the frameworks as well as the popularity of the frameworks ISO 14001, ISO 26000 and SA8000 have been selected for the Sustainable Development Maturity Model for respectively Environmental Conditions, Social Conditions and Worker Conditions. From the selected frameworks Key Sustainability Activities and Activities belonging have been identified. It appeared that a number of Key Sustainability Activities was overlapping and thus choice have been made to exclude certain aspects to prevent doubles. For all Activities definitions have been made as well as a descriptor for each Activity. For the Social Conditions also definitions have been made for the Topics as well as a descriptor for the Topics to show that it is possible to work on this level of detail within the Sustainable Development Maturity Model. The found Key Sustainability Areas and Activities have been validated using publications of several well-performing companies (by means of sustainable performance). As soon as the maturity of an organization for different aspects has been determined the organization may decide to work on certain aspects. For this several practices in order to improve the maturity of the organization have been suggested. Within this research changes for three different fields of organizational improvement have been suggested: firstly an overview of aspects to improve the organizational performance of an organization, secondly the improvement of organizational processes, including a new organizational structure and thirdly by looking to the organizational learning processes. A reflection of how these practices can be used have been given as well as an overview of how aspects to improve the organizational performance can specifically be used to improve the performance of an activity or topic from one level to another. Finally a concept version of the model has been made using Microsoft Excel showing that it is possible to build the model with previous steps. A reflection has been given on the use of the model and on the challenges and limitations as identified in the introduction of the thesis. A total overview of the model in one figure has been given showing the relation between the different steps. This thesis ends with the conclusion that it is possible possible to combine insights from the field of the Capability Maturity Model with insights from the field of Sustainable Development. In further research the Sustainable Development Maturity Model should be further developed and it should be determined if the model has an added value for the sustainable management and performance of an organization.