In the context of modern approaches to quantum physics via two-state systems, the question of tools for assessing students’ understanding and for identifying learning difficulties in quantum physics arises anew because these differ from traditional approaches. In addition, there are different two-state approaches with different characteristics. One of the key points for understanding quantum physics is the measurement process as it lies at the heart of the differences between quantum and classical physics. Therefore, assessing students’ conceptions about the measurement process was regarded as a first step towards a comprehensive quantum concept inventory. Hence, a questionnaire to inquire the students’ perspective and reasoning about the measurement process as a key concept in quantum physics was developed and presented. This contribution will describe first results of its evaluation and give hints to its further development.