  In order to commemorate Alfred Land\'e's unriddling of the anomalous Zeeman
Effect a century ago, we reconstruct his seminal contribution to atomic physics
in light of the atomic models available at the time. Land\'e recognized that
the coupling of quantized electronic angular momenta via their vector addition
within an atom was the origin of all the apparent mysteries of atomic structure
as manifested by the anomalous Zeeman effect. We show to which extent Land\'e's
ideas influenced the development of quantum physics, particularly Wolfgang
Pauli's path to the exclusion principle. We conclude with Land\'e's brief
biography.
