This is a collection of contributed papers by former collaborators and colleagues of Claudio Bunster (formerly Teitelboim). The topics include General Relativity, Quantum Gravity, String Theory; from historical reviews to current research; from mathematical structures underlying the fundamental interactions, to cosmological scenarios describing the universe at its birth. Each contribution covers a topic in a self-contained manner, including all the references and illustrations to make it easy to read separately. The volume covers a number of important topics in theoretical physics of the last 30 years. Many of the seeds of string theory like supergravity, the AdS/CFT correspondence, p-form fields, electric-magnetic dualities, were discovered first in the context of gravitation by Bunster and his collaborators. This volume is rooted in this tradition and makes it an interesting source for theoretical physicists engaged in current research.