"Market Systems Development (MSD) is an approach to poverty reduction that aims to create long-lasting and large-scale change by stimulating more inclusive growth. To achieve a systemic change vision, market systems programmes often partner with the private sector to introduce new or improved business practices, products and services. Understanding the mechanics of these business models is at the heart of programme success. This paper presents a framework for assessing the efficacy of business models. To help future practice be grounded in reality, we have included detailed business model cases studies from market systems programmes in Afghanistan, Zambia, Kosovo and Nigeria. The paper ends by extracting five key lessons for implementers to improve the way in which they engage with the private sector in building 'win-win' models."