Boundaries are a popular topic among organizational researchers, many of whom argue that over the past decade we have witnessed a trend toward permeable boundaries and in some cases a blurring between organization and environment. Contrary to received wisdom, we argue that the question as to whether organizational boundaries have become more permeable or not cannot be decided empirically but is mainly a theoretical issue. Whether or not data indicate permeability or impermeability depends on the theoretical lens employed. Against this backdrop, we review how two prominent approaches to the study of boundaries, sociological systems theory and new institutionalism, not only arrive at different conclusions but also mandate diverging avenues of research. We focus in depth on several empirical trends: advances in information and communication technologies, increasingly dynamic fields and markets, invasive transparency regimes, and metaorganizations. We then introduce the contributions in this volume, showing how they elaborate on these and other empirical trends, drawing on different theoretical perspectives, to advance our understanding of the importance of boundaries within and around organizations.