This document discusses approaches to combining datasets from multiple trusted research environments for federated analysis. It describes several approaches: the Linked Data approach which uses Semantic Web standards to represent data; the OMOP CDM approach which uses a common data model format; the Custom API approach which uses APIs to share specific data points; the Dedicated Environment approach which connects environments through a dedicated network; and a Hybrid approach combining aspects of different methods. Each approach has advantages and challenges to consider for different federated analysis use cases. Other factors like data anonymization, versioning, and security also need to be addressed.