Can mini grids help to solve the problem of poorly served main grid connected communities? A mini grid is an electricity generation and distribution network that supplies electricity to a localized group of customers. Mini grids can be isolated from or connected to the main grid. To date, most mini grids in Sub-Saharan Africa have been built in electrically isolated rural villages not connected to the main grid. Based on broad experience working with mini grid programs in more than 20 low- and middle-income countries and five detailed case studies, the authors offer observations and recommendations about mini grids in general and a new type known as “undergrid mini grids” being used in Nigeria and India to serve poorly served communities.