Classification and output of multiple ethnicities: issues for monitoring Māori health was produced as part of a broader project funded by Te Kete Hauora, Ministry of Health to investigate issues with ethnicity data in New Zealand and the implications of these for the Māori health and disability sector. The paper is one in a series of topic-based discussion papers. This paper broadly considers the conceptualisation and classification of multiple ethnic affiliations in New Zealand, and different methods for the collection, classification, analysis, and output of data on multiple ethnicities in the health sector, with the aim of identifying practical and theoretical issues that impact on the ability to measure and monitor Māori health and ethnic inequalities.