The choosing methods and techniques section of the GUIDE is concerned with methods and tools (or techniques) in evaluation. Here we focus mainly on the roots or foundations that underpin these methods and tools. First five broad methodological positions are described, then the way these connect to more general philosophical schools that are debated within most applied social and economic sciences are discussed. Many of these philosophical debates highlight the centrality of theory in evaluation which has become increasingly important in recent years. For this reason we briefly review why theory matters in the evaluation of socio-economic development and the different forms it can take. These methodological and philosophical foundations support some of the main categories or families of method that will be discussed in The choosing methods and techniques section of the GUIDE and are introduced here.