  Radioactivity was discovered as a by-product of searching for elements with
suitable chemical properties. Understanding its characteristics led to the
development of nuclear physics, understanding that unstable configurations of
nucleons transform into stable end products through radioactive decay. In the
universe, nuclear reactions create new nuclei under the energetic circumstances
characterising cosmic nucleosynthesis sites, such as the cores of stars and
supernova explosions. Observing the radioactive decays of unstable nuclei,
which are by-products of such cosmic nucleosynthesis, is a special discipline
of astronomy. Understanding these special cosmic sites, their environments,
their dynamics, and their physical processes, is the `Astrophysics with
Radioactivities' that makes the subject of this book. We address the history,
the candidate sites of nucleosynthesis, the different observational
opportunities, and the tools of this field of astrophysics.
