To remain competitive, organizations need to continuously develop their knowledge. While knowledge work is performed similarly in organizations across different sectors, the measurement and assessment of its results currently lacks standardized approaches. This paper sets out to identify indicators that are suitable for making knowledge development transparent to support monitoring of knowledge work. Therefore, a multi-phase mixed methods approach was chosen. In a series of three studies, an activity-focused perspective towards knowledge work was adopted, where knowledge is viewed as passing through a phased maturing process. An initial set of indicators was identified in an ethnographically-informed study and subsequently refined in an online survey. In the interview study, data was collected from 121 European organizations of different sizes, sectors and knowledge-intensity. Feedback from respondents provided evidence for the suitability of items for indicating knowledge maturing and revealed a structure of five factors that were labeled, interpreted and discussed.