In 1926 E. Schrödinger introduced the equation obeyed by the de Broglie waves, and he demonstrated that the quantization conditions emerge from the solution of the eigenvalue problem for his wave equation. He applied his equation to the hydrogen atom and he found that both the quantization of angular momentum and the quantization of energy emerge from his equation. The Schrödinger equation describes the behavior of quantum particles by means of waves and thereby reconciles, in a consistent manner, the wave / particle duality.