Summary Introduction Why food composition databases are important How food composition databases are produced Considerations in the use of food composition databases Conclusions and future role of EuroFIR Acknowledgements References and further reading SummaryFood composition data are fundamental to the quantitative study of nutrition and are widely used in a variety of fields, including public health. However, knowledge of both the compilation and the limitations of food composition databases, which contain information on the concentrations of nutrients in food, is beneficial to ensure that users understand how to utilise the data appropriately. This guide provides background information on the importance of food composition data, and then explains the processes involved in producing and compiling these data. It then offers guidance on some of the key issues that users should be familiar with when using andmanipulating food composition data. Suggestions for further reading are given for users who may need more detailed information on specific topics and the resources produced by the EuroFIR (European Food Information Resource) Network of Excellence are highlighted.