Volume 7 is a direct continuation of Volume 6, which documented the birth of the complementarity argument and its earliest elaborations. It covers the extension and refinement of the complementarity argument from 1933 until Bohrs' death in 1962. All Bohr's publications on the subject, together with selected manuscripts and extracts of his correspondence with friends and fellow pioneers such as Werner Heisenberg and Wolfgang Pauli, are included. Divided into two, largely independent parts, the volume begins with Bohr's contributions to "Relativistic Quantum Theory". Together with Léon Rosenfeld, Bohr undertook a thorough investigation of the measuring problem in quantum electrodynamics and demonstrated the full accordance between the formalism and the result of idealized thought experiments.
The articles in the second part, although also restricted in scope to the field of physics, address a broader audience. One of the most impressive treatises is Bohr's own account of his debates with Albert Einstein, over more than twenty years, on the consistency, the completeness and the epistemological consequences of quantum mechanics.
Volumes 6 and 7 of the Collected Works are in turn related to the forthcoming Volume 10 which broadens the scope by presenting Bohr's applications of the complementarity argument beyond the domain of physics. Although each volume may be read independently, careful attention should be paid to the interrelationships between each volume in order to appreciate the subtlety of Bohr's continued elaboration and fine-tuning of his complementarity argument.