This volume brings together interdisciplinary topics in condensed matter theory and related disciplines, with an emphasis on the common concerns of (mostly) theorists applying advanced many-particle methods in diverse areas: solid state and low temperature physics; atomic, sub-atomic, and statistical physics; engineering sciences, keeping a sharp focus on theoretical developments which cross borders between subfields of condensed matter physics and which provide new approaches to outstanding problems. The book records the fascinating variety of new results associated with the idea of similarity in diversity. In perusing this volume, the reader will be stimulated to discern threads of similarity in the great diversity of physical phenomena and theoretical models proposed to explain them; and indeed there are threads that can be glimpsed in the table of contents, and ramifications of these threads as one reads through the articles. One conclusion is clear: the search for similarity in diversity is a powerful approach to interdisciplinary science.