The development and diffusion of environmental technologies, which is considered to be one way of achieving the dual goals of maintaining competitiveness in a dynamic and knowledge-based economy while integrating environmental consideration in this process, may be influenced by a number of sector-specific conditions. In light of this, case studies of energy efficiency innovations in the Nordic building sector were carried out as a part of two-year research project on Green Market and Cleaner Technologies - Leading Nordic Innovation and Technological Potential for Future Markets. The studies looked into the characteristics of the industry as well as other issues influencing the three key activities of an innovation system - access to knowledge, access to resources and market formation. This report highlights some features of the building industry as well as their products which tend to pose constraints to the three innovation activities in the sector. It elucidates several strategies deployed by innovating companies to overcome some of the constraints and points to specific areas for policy interventions needed to effectively enhance innovation activities in the sector.