A common definition of astroparticle physics has emerged in the last 5 years essentially through the road-mapping exercises in Europe and the US.  What seemed before as a series of independent interdisciplinary endeavours appears today as a relatively unified domain, with common themes, complementary approaches and many common experimental techniques. This domain continuous to have of course porous frontiers with the traditional disciplines that permitted its appearance (astrophysics, particle physics, nuclear physics, etc.)
The domain develops around 3 major questions (they form the 3 chapters of my presentation)

1. What is the matter/energy content of the Universe?  In particular what is the nature of dark matter/energy and inflation.
2. What is the influence of the high-energy phenomena in the formation of large cosmic structures? In particular can we disentangle the presence of new particles and/or the violation of known laws by studying the high-energy particles and radiation that they emit?
3. What is the exact form of matter and interactions at the highest energy scales, beyond these accessible to accelerators?  In particular can we probe the grand unification scales through the study of extremely rare phenomena as proton or double beta decay obtaining thus access to inflation-scale physics and the mechanisms giving a mass to the neutrino?

I will describe the main issues of each question and the experiments/observatories that currently tackle the problems as well as these that are projected in the near and mid-term future. I will give particular emphasis to the problems that span all three questions unifying the domain (dark matter indirect and direct detection, multi-messenger complementarities, importance of the neutrino mass and proton decay to the other fields, etc.) being aware of course that many issues concerning question 2 will be dealt in detail in other lectures of the school, I will only briefly sketch the transversal issues relating the middle question  with the other two.
If there is sufficient time, I would also like to touch the point of the possibilities that astroparticle physics infrastructures, by covering large areas with sensors, or attempting extreme radiopurities,  open for other sciences: e.g. geosciences and environment.

• Astrophy..
  
• .