That part of science which is known as Nuclear Physics is, like all live research areas, constantly evolving as progress is made and new frontiers open up. In the past Nuclear Physics could be defined simply as the science of the atomic nucleus. The features observed and the associated forces were found to differe so drastically from what could be studied in other systems that both the identity and the fundamental character of that science were established beyond any doubt. Furthermore, it was assumed, sometimes implicitly, that the nucleus provided us with a specific field where one could study the strong interaction, one of the fundamental interactions at work in nature. Yet, it is clear now that this interaction, although it plays an essential role in nuclei, does not appear in all its clarity but intervenes only through that part of the force which spills out of the quark bag.
Thus, in retrospect one can only wonder at the quality and predictive value of nuclear models which have been elaborated over the last 40 years. Yet, al least for the time being, a global description of nuclei cannot be formally and directly derived from a fundamental interaction. Frustated in its ambition to be the field where the fundamental strong interaction could be elucidated, Nuclear Physics has actually developed into a very original and fundamental branch of science, the science of complex systems of elementary particles.