The thesis begins with a discussion of causality as used in Physics. It distinguishes between two kinds of causes, the efficient and the formal, and argues that though the latter has always existed in Physics, it has remained mainly on the tacit level. It goes on to point out that the formal cause is of particular importance to quantum mechanics and unless it is introduced explicitly and on the same footing as the efficient cause, paradoxical and intuitively unintelligible results are likely to appear. Indeed, one such result is the Aharonov-Bohm effect where the vector potential seems to play an ambiguous role. The second chapter examines some of the attempts to explain this effect and comes to the conclusion that it cannot be done by forcing the problem into the existing formalism. Rather, a more radical approach is needed based on the formal cause. Chapter three takes a closer look at the effect with a view to understanding more clearly its structural features, a necessary preparation for the introduction of the formal cause. Chapter four examines cases whose forms are analogous to that of the Aharonov-Bohm effect in order to gain some insight into the features which might be used for a structural reformulation of that effect. Finally, chapter five attempts a mathematical approach based on the formal cause. This is first applied to the classical cases of a particle inside and outside an electromagnetic field where use is made of global referentiframes. The Aharonov-Bohm effect is then treated by replacing the referential frames by the quantum potential. The structural features of the latter are examined in detail with the help of computer generated three-dimensional plots. These results predict clearly visualisable changes of symmetry, brought about by the vector potential, which affect the distributions of well defined particle trajectories. The chapter is concluded with a brief outline of other applications of the structural approach