In the networked information and knowledge-based economy and society, the notions of ‘open’ and ‘openness’ are used in a variety of contexts; open source, open access, open economy, open government, open innovation – just to name a few. This paper aims at discussing openness and developing a taxonomy that may be used to analyse the concept of openness. Are there different qualities of openness? How are these qualities interrelated? What analytical tools may be used to understand openness? In this paper four qualities of openness recurrent in literature and debate are explored: accessibility, transparency, participation and sharing. To further analyse openness new institutional theory as interpreted by Williamson (2000) is used, encompassing four different institutional levels; cultural embeddedness, institutional environment, governance structure and resource allocations. At what institutional levels is openness supported and/or constrained? Accessibility as a quality of openness seems to have a particularly strong relation to the other qualities of openness, whereas the notions of sharing and collaborative economics seem to be the most complex and contested quality of openness in the knowledge-based economy. This research contributes to academia, policy and governance, as handling of challenges with regard to openness vs. closure in different contexts, territorial, institutional and/or organizational, demand not only a better understanding of the concept, but also tools for analysis.