After decades of its development, Islamic economics still remains challenged whether it is qualified to be a discipline. Islamic economics is not only expected to offer a new perspective in understanding economic phenomena and solutions. Islamic economics as a discipline is also challenged to solve the problems based on its own scientific foundations and philosophy that would characterize its approach, and is also challenged to be able to survive with knowledge accumulation and progress. This chapter offers an usul a-Iqtisad as an approach to develop the foundations of Islamic economics based on the provisions sources of knowledge in Islamic epistemology and Islamic ontological principles of how to understand economic phenomena. In usul al-Iqtisad, the effort to develop Islamic economics discipline can be done in three stages, namely establishing the foundations of Islamic economics discipline, developing the scientific conceptual scheme of Islamic economics, and constructing discipline of Islamic economics and its body of knowledge. Usul al-Iqtisad offers a comprehensive approach beyond “juridical texts analysis” or fiqhi implications as studied in usul al-fiqh approach. The term iqtisad used rather than fiqh is to emphasize that we are not dealing with the legal aspects of decision-making per se, but a much wider area of human behaviour and social system in developing Islamic economics as a system of thought and systematic discipline