  The production of about half of the heavy elements found in nature is
assigned to a specific astrophysical nucleosynthesis process: the rapid neutron
capture process (r-process). Although this idea has been postulated more than
six decades ago, the full understanding faces two types of uncertainties/open
questions: (a) The nucleosynthesis path in the nuclear chart runs close to the
neutron-drip line, where presently only limited experimental information is
available, and one has to rely strongly on theoretical predictions for nuclear
properties. (b) While for many years the occurrence of the r-process has been
associated with supernovae, more recent studies have cast substantial doubts on
this environment. Alternative scenarios include the mergers of neutron stars,
neutron-star black hole mergers, but possibly also rare classes of supernovae
as well as hypernovae/collapsars with polar jet ejecta and also accretion disk
outflows related to the collapse of fast rotating massive stars with high
magnetic fields. Stellar r-process abundance observations, have provided
insights into, and constraints on the frequency of and conditions in the
responsible stellar production sites. One of them, neutron star mergers, was
just identified and related to the Gravitational Wave event GW170817. High
resolution observations, increasingly more precise due to improved experimental
atomic data, have been particularly important in defining the heavy element
abundance patterns of the old halo stars, and thus determining the extent, and
nature, of the earliest nucleosynthesis in our Galaxy. Combining new results
and important breakthroughs in the related nuclear, atomic and astronomical
fields of science, this review attempts to provide an answer to the question
"How Were the Elements from Iron to Uranium Made?" (Abridged)
