The informal housing practices in the North, while still perceived as a niche phenomenon in policy sphere, gain wider recognition in contemporary urban and housing studies. This introduction discusses the relevance of such practices within the housing landscape of big urban centres and reflects on the main theoretical considerations in their study. In particular, it reflects on the shifting boundaries of understanding of the formality-informality continuum as it unfolds across state, market and people's actions in the diverse contexts discussed in this volume.