This Implementation Guide defines common FHIR extensions and components that are standardised for reuse across multiple Australian Digital Health Agency (ADHA) Implementation Guides. It establishes consistent ways to capture and exchange common data elements that appear frequently across different healthcare contexts. Rather than each ADHA Implementation Guide defining these elements differently, this guide provides standardised definitions that ensure consistency and interoperability. When multiple ADHA Implementation Guides need to capture the same types of information, they all reference the same standardized extensions defined here. This approach promotes consistency across ADHA's suite of Implementation Guides and ensures that healthcare systems can exchange information reliably across different use cases within Australia's digital health ecosystem. 