Denmark and other countries have the ambition to move towards a sustainable transport system. However it is challenging to achieve and credibly demonstrate progress towards sustainability in transport. The paper will specify foundations for monitoring and reporting progress towards sustainability in the Danish transport policy, using policy goals, sustainability indicators and performance measures. The paper represents a first step in the SUSTAIN project aiming to develop a framework for national sustainable transport planning. The paper will draw on analysis of experience with the development and use of sustainability indicators to report transport policy performance, in Europe, North America and other parts of the world. The experience will be connected to critical literature in the areas of sustainability theory, knowledge utilization, and implementation in order to identify challenges to overcome for a Danish approach.