This chapter presents a research study on trust in sources of knowledge for teachers’ continuing professional development (CPD), comparing two national contexts, Germany and Sweden. From the vantage point of the project’s findings, considerations are made about trust in institutions, which for example offer CPD for teachers, and trust as a property in school systems. Examining trust relationships beyond the individual school community requires an understanding of the effect of nation-specific particularities on the emergence of trust. This chapter proposes to focus on the trustworthiness of institutions from the teachers’ perspective. It is argued that trustworthiness can be partly measured through the same categories that are demonstrated to be productive for examining relational trust, as proposed by Bryk and Schneider (Trust in schools. A core ressource for improvement, New York, Russell Sage Foundation, 2004), including perceived competence, understanding and respect of others. It is furthermore argued that trust and trustworthiness in school systems should be investigated by comparative case study designs that depict trust as an aspect of complex interrelated systems in different contexts. In addition, in order to understand trust as property of systems, data are required that capture the collective voice of the teaching profession. With respect to the proposed case study, the findings of the questionnaire study must then be interpreted in both a case and a socio-historically sensitive manner, in order to give meaning to similarities and differences of trust between the countries investigated. Finally, also drawing on Bryk and Schneider (Trust in schools. A core ressource for improvement, New York, Russell Sage Foundation, 2004), this chapter suggests different categories of trust that can contribute to a conceptualisation of diverse context-specific trust patterns. These are illustrated by examples taken from the German and Swedish cases.