  This volume covers one of the most thrilling two-year periods in
twentieth-century physics, as matrix mechanics - developed chiefly by W.
Heisenberg, M. Born, and P. Jordan - and wave mechanics - developed by E.
Schr\"odinger - supplanted the earlier quantum theory. The almost one hundred
writings by Einstein, of which a third have never been published, and the more
than thirteen hundred letters show Einstein's immense productivity and hectic
pace of life.
  Einstein quickly grasps the conceptual peculiarities involved in the new
quantum mechanics, such as the difference between Schr\"odinger's wave function
and a field defined in spacetime, or the emerging statistical interpretation of
both matrix and wave mechanics. Inspired by correspondence with G. Y. Rainich,
he investigates with Jakob Grommer the problem of motion in general relativity,
hoping for a hint at a new avenue to unified field theory.
  Einstein falls victim to scientific fraud when, in a collaboration with E.
Rupp, he becomes convinced that the latter's experiments, aimed at deciding
whether excited atoms emit light instantaneously (in quanta) or in a finite
time (in waves), confirm a wave-theoretic explanation.
  While it was known that the teenage Einstein had been romantically involved
with Marie Winteler in 1895, newly discovered documents reveal that his love
for Marie was rekindled in 1909-10 while he was still married to Mileva
Mari\'c.
  The 1925 Locarno Treaties renew Einstein's optimism in European
reconciliation. He backs the `International manifesto against compulsory
military service' and continues his participation in the League of Nations'
International Committee on Intellectual Cooperation. He remains intensely
committed to the shaping of the Hebrew University in Jerusalem, although his
enthusiasm for this cause is sorely tested.
