Network Paper 69 summarises the basic characteristics of a Common Needs Assessment and reviews experience in using assessments in recent years. The authors note that while good CNAs can help to develop a better joint understanding of needs, capabilities, and appropriate response, in trying to meet too many objectives, CNAs have sometimes failed to live up to this potential. Carrying out a CNA takes time and resources; even when funds and experienced assessors are available, results have not always been useful or timely. Drawing on field experience from more than a dozen CNAs, this paper identifies the opportunities, costs and trade-offs involved in carrying them out and provides an overview of steps which can be taken to avert common problems.