We review some among the many trends in the foundations of physics. Reductionism is a traditional one: new milestones have been achieved in the recent past but puzzling aspects are accompanying the confinement properties of quarks. New achievements and persisting open problems characterize unified theories of the known basic interactions. An impressive accumulation of experimental results on the fundamental aspects of quantum behaviour came in the last few years; the variety of domains where quantum phenomena are currently investigated is extending beyond expectations. Remarkable developments in the mathematical foundations of quantum mechanics have accompanied the last decades and still characterize many branches of intense research work.