This book traces the evolution of the ideas that eventually resulted in
the elementary quantum theory in 1925/26. Further, it discusses the
essential differences between the fundamental equations of Quantum
Theory derived by Born and Jordan, logically comprising Quantum
Mechanics and Quantum Optics, and the traditional view of the
development of Quantum Mechanics. Drawing on original publications and
letters written by the main protagonists of that time, it shows that
Einstein's contributions from 1905 to 1924 laid the essential
foundations for the development of Quantum Theory. Einstein introduced
quantization of the radiation field; Born added quantized mechanical
behavior. In addition, Born recognized that Quantum Mechanics
necessarily required Quantum Optics; his radical concept of truly
discontinuous and statistical quantum transitions ("quantum leaps") was
directly based on Einstein's physical concepts.