This document discusses the development of a Transboundary Diagnostic Analysis (TDA). It outlines the steps to develop the TDA, including defining system boundaries, collecting and analyzing data, identifying and prioritizing transboundary problems, determining the impacts of priority problems, analyzing causes of problems, and developing thematic reports. It also discusses that the TDA provides factual basis for the strategic planning component and should involve engagement with stakeholders throughout the process. Finally, it notes that the TDA development team should be representative of participating countries and stakeholders.