This chapter serves as an introduction to the methodological framework of the What’s the Evidence research project, a complex, mixed-methods four-year research study. The research was structured in three phases and engaged teachers, educational leaders and researchers as participants. In 2021, the first phase of project commenced with the proposition of a Teacher Quality Construct informed by indicators collected from grey literature. A scoping review of academic literature was used to establish a scholarly, research-informed evidence base for the Teacher Quality Construct. Through the second phase in 2022, the researchers tested the construct for fit for purpose for use with early career teachers adopting a modified Delphi process. The third and final phase commenced in 2023 and focused on testing a sample of these indicators, adopting measurement tools identified as valid in the scoping review process. Discussion and survey tools informed a standard setting exercise undertaken with groups of teachers and principals. Data collected from these participants was analysed using processes based on modern measurement theory as part of a detailed research design process, aiming to test the predictive validity of a Teaching Performance Assessment against a research-informed construct of teacher quality.