Advances in research in finite-size systems (including atomic, molecular and compound clusters and inorganic nanometer particles) continue ti stimulate researchers to address a number of fundamental and conceptual questions in this field. Since 1985, the TSRC workshops on clusters have focused on topics from this field, by discussing selected mathematical-physical and chemical questions, including phase-changes (both dynamical and equilibrium aspects), quantum size effects, size-scaling toward bulk properties, many-body quantum states, solvation dynamics and electrodynamics, and caging of chemical reactions. In keeping with the spirit of the TSRC workshops, the 1991 meeting will again bring together, in an informal setting, a group of literature-familiar scientists in the field for extensive discussion on a set of currently opened questions.