"Micro, small and medium private and social enterprises (hereafter referred to as 'enterprise') are emerging as important players in enabling or delivering sustainable water, sanitation and hygiene (WASH) services. This area is highly dynamic, thus pointing to a need for recent consolidated evidence about the effectiveness, sustainability and quality of services provided by such enterprises. A synthesis of literature on small-scale sanitation entrepreneurs was conducted in 2008, and at that time reported that the "quality research was relatively scarce, and few good case studies were found" (Valfrey-Visser and Schaub-Jones 2008, p.4). This paper reviews literature over the five years since 2008, once again taking stock and examining the nature and quality of the evidence for private enterprise engagement across both sanitation and water sub-sectors. In particular, we review of the evidence concerning if and how poor households and communities are being supported."