Experimental and phenomenological approaches to the structure of exotic nuclei

The structure of exotic nuclei that will become accessible with radioactive beams, especially in extremely neutron-rich nuclei where there is a large ``lever arm`` from the valley of stability, is likely to be quite different from anything we have yet encountered. There have been suggestions of radically-different shell structure due, for example, to more-rounded shell potentials (no ``l{sup 2}`` term in the Nilsson potential) or to weaker l{center_dot}s interactions. Also, the weak binding of the outermost nucleons, the coupling to the continuum, changes in residual p-n and pairing interactions, will all contribute to new types of structure and collectivity. Among other effects, magic numbers are likely to lose their robustness; sequences of shell model orbits might be altered in major ways; the onset, manifestations, and evolution of collectivity could be different; unique parity orbits may revert to their parent shells. Radioactive beams will provide the opportunity to study these exotic nuclei, but, at the same time, the amount of data obtainable win be much less than we are accustomed to. Hence, it will be necessary to develop highly-efficient experimental approaches on the one hand, and new signatures of structure, based on the simplest-to-obtain data, on the other. Recently, progress has been made in both areas, and this work is discussed below