The design, monitoring and impact assessment of development programmes generally require the use of socio-economic surveys. The quality and reliability of the data depend on a large number of factors that are not always obvious and may vary according to the context. In this respect, rural Africa has its own particular characteristics, and failure to take these into account can seriously compromise the results. This guide, based on extensive field experience in West Africa and Senegal in particular, provides practical advice on designing, conducting and using surveys to minimise the risks associated with the GIGO (Garbage In - Garbage Out) phenomenon.