The past ten years or so has seen a rapid increase in the number and size of non-profitorganisations involved in development work, commonly known as NGOs (Non-governmentalOrganisations). This growth has not always been accompanied by an improvement in their performance. In fact, there are signs that a rapid expansion of the NGO sector may be lowering its quality overall, partly because organisations are started by people with limited or no experience of the voluntary sector or its principles. While this publication is intended to be a practical guide for use by NGOs themselves, it is assumed that the process is facilitated by a skilled adviser or consultant. Too often, NGOs try to assess their organisation by a process of self-reflection alone and it just doesn't work well. These guidelines begin with the key principles that have to be applied and preconditions which have to be in place if a self-assessment exercise is going to be effective. Then, the whole idea of organisational capacity is discussed. This base is used to explain how a participatory process of facilitated capacity assessment can be carried out for NGOs with low, medium and high complexity. Appendices contain practical materials referred to in the text.