The author introduces the term ‘judicial engagement’ to conceptualize the interaction between different international courts. Judicial engagement occupies a large middle ground on the continuum between resistance and convergence, highlighting the willingness of the participating adjudicators to consider external sources in the appropriate case, denoting commitments to judicial deliberation but being open to the outcome of either harmony or dissonance. This chapter focuses on two specific research questions. Firstly, it searches for the normative grounds for this adjudicative behaviour, identifying the elements that support it, as well as those that render ‘cross-judging’ impossible. The second question to be answered is the possible function and contribution of engagement between trade and investment tribunals. The ultimate enquiry concerns whether we should or should not promote this adjudicative behaviour. If so, what would its benefits be? The discussion in this regard will look into the possible function of judicial engagement in the light of the legitimacy challenges currently faced, and the role of governance currently performed, by the tribunals involved.