In this book, Yuval Neeman and Yoram Kirsh recount the story of particle physics in the twentieth century. They explain how physicists first discovered the various levels of the atom and then tried to describe its structure, culminating in the most recent "standard model". Assuming that the readers knowledge of physics is limited to basic notions such as energy, mass, and electrical charge, the authors explain the theory of relativity and the fundamental principles of quantum mechanics, which have guided physicists in their search for the ultimate particles of matter. Yuval Neeman teaches theoretical physics at the University of Tel Aviv. Yoram Kirsh teaches physics at the Open University of Israel.