In 2013, the Secretary-General of the UN named eight institutions as models for considering intergenerational solidarity and representing the interests of future generations in policy making. Each institution has its own unique set of characteristics as a result of constitutional backgrounds, functions, and organisational structures, to name only a few characteristics. Additionally each institution has found its own set of theoretical bases and principles upon which to pursue its activities and reach its goals. This comparative study of the model institutions is to identify the set of most important features, including not just references to legal framework, organisational structures, but also missions, aims, and goals, and theories and principles by which they can be characterised. This will be done by placing each institution within this set of criteria, assessed and drawn from existing practice, in which links between the various aspects are highlighted, and it is shown how theories can be operational in practice. The chapter argues for and reflects on the innovative characteristics of model institutions for sustainable development when the theoretical basis – especially legal theory – is lagging behind.