ABSTRACT
We can summarize the situation in particle physics at the end of the 1960s as follows. Experimental methods had made immense progress since the middle of the century, but theory had failed to keep up-only purely electromagnetic phenomena could be described in a truly satisfactory way. There was a very successful descriptive field theory for the weak interactions, but it was not satisfactory, since it was not renormalizable. The situation was even worse in the realm of the strong interactions. The dream that a completely new approach would be provided by the bootstrap method failed to bear fruit, and the quark model, which did describe some phenomena quite well, was far from being a consistent theory. Great progress had been made in the classification of particles through symmetry considerations, but a dynamic foundation for the symmetries was lacking.
