Can the 'measurement problem' in quantum physics be resolved? What essential principles must an interpretation of quantum mechanics uphold in order to be satisfactory, and is it possible to preserve them all? This proposal is for a 2 year research project on these questions. The main aims are: to clarify what each existing approach assumes about the second question above, and argue for the essential role of causality here; to propose and work on a new path to a satisfying, causal understanding of QM, based on preserving relativistic causality in a new form by introducing a third truth value. The project involves one principle researcher who will be based at Imperial College, London. The novel theoretical work will be carried out at Imperial and during travel to attend conferences, give seminars and discuss the ideas. The expected outputs are 7 research papers which will compare existing approaches on grounds of causality, discuss what is essential and inessential, and propose the new course to a satisfying interpretation. The outcomes should be: a clarification of the disagreements between the various existing programs, leading to more explicit and fruitful debate; the advancement of a relativistic causality principle that can be satisfied by quantum mechanics; a new way to model quantum systems, which will be the foundation for a new causal interpretation of QM. By reestablishing a rigourous notion of causality, the principle researcher hopes to establish a program that can give a "third way" between operationalist and traditional "hidden variables" accounts of QM, and provide a physical principle-driven derivation of essential aspects of QM, which will open up new possibilities and spark further progress, for instance in the currently intensely studied quesition of what physical principles can explain the limitations on quantum "non-local" correlations.