This article deals with the systems level in Freeman and Perez's innovation typology (incremental, radical, system, techno-economic paradigm). Transitions at this level are understood as changes from one socio-technical system to another, involving co-evolution of technology and society. To understand these transitions, the article describes a multi-level perspective, based on insights from sociology of technology and evolutionary economics. This perspective is used to analyse a detailed historical case study, the transition from surface water to piped water and personal hygiene (1870-1930). By the middle of the 19th century, problems in the water supply regime grew worse, as expanding urban populations dumped their waste in canals and surface waters. Local conditions in some specific cities provided space for the first piped water systems in the 1850s. Problems in the water supply regime grew worse in the 1860s and 1870s, but public authorities in other cities did not embrace the new niche. Instead, they searched for solutions within the existing regime. Only after wider landscape developments in the 1880s and 1890s (economic, cultural, political) could the niche break through and trigger wider transformations. So external macro-developments played a crucial role in the take-off and diffusion phase of this transition. This transition is a good example of co-evolution of technology and society, involving technological innovations, such as piped water infrastructure, soap, toilets, baths, as well as cultural, political, economic and behavioural changes. The case study illustrates how the multi-level perspective can be used to analyse how these changes influenced each other in a co-evolution process. The article thus fits in the growing literature on co-evolution. While most literatures look at co-evolution between two or three aspects, this article develops a broader understanding of co-evolution. © 2005 Elsevier Ltd. All rights reserved.