This chapter provides suggestions of how the international classification of functioning, disability and health for children and youth (ICF-CY) can be used in various services for children and youth with disability. The ICF-CY classification is recognised as a means to identify what is measured in the assessment of a child's functioning by allowing the identification of content in specific measures. The chapter describes reduced sets of ICF-CY codes with the purpose of limiting the exhaustiveness of the classification. Core and code sets developed internationally by the selection of appropriate categories for specific purposes are presented with complete information on availability. The ICF-CY classification has been used as a mean to identify and compare content in commonly used measures. By linking assessed variables with the ICF-CY language, the framework can serve an organising tool to document the content included in existing tools. Despite the benefits of the ICF-CY, the classification with its many categories can be a practical challenge.