OVERVIEW The field of High Energy and Astroparticle Physics aims at unraveling the laws of physics at the shortest distance scales and how these give rise to the universe we live in. Up to the highest energies that can presently be created by man-made accelerators, nature is remarkably well described by a single theory, the standard model of particle physics. The electromagnetic, weak and strong interactions among the elementary fermions are well described by a quantum field theory merging quantum mechanics and special relativity, and incorporating the principle of gauge symmetry. In the Standard Model of particle physics the basic forces other than gravity are mediated by the exchange of intermediate vector bosons associated to the standard model gauge symmetry: the photon, the gluons and the electroweak bosons. The theoretical formulation of the Standard Model was developed from the mid to late 20th century, and its current form has gained general acceptance after the experimental confirmation of the existence of quarks in the mid 1970s. The gauge bosons associated to the electroweak gauge symmetry, the photon and W and Z gauge bosons, were directly produced for the first time at CERN in 1983, while the gluons are associated to the SU(3) color symmetry and were already discovered in the late 1970s. Today we know for certain that there are at least three types or “generations” of elementary constituents of matter. The simplest way to provide masses for the W and Z bosons as well as for the charged fermions is to spontaneously break the gauge symmetry down to the color and electromagnetic subgroup. This suggests the existence of a physical elementary scalar particle, the socalled Higgs boson, which is indeed part of the Standard Model, and whose recent discovery at the Large Hadron Collider (LHC) experiment at CERN by the ATLAS (see Figure 1) and CMS Collaborations constitutes an outstanding achievement in particle physics, and a triumph for theory. The recent experimental confirmation of the existence of the Higgs boson has put the Standard Model on a very firm footing. However, there are several reasons why the Standard Model is believed to be incomplete and even within the Standard Model many puzzles remain. One of these puzzles, for example, involves the neutrino sector. Among the elementary constituents of matter neutrinos are unique in that they do not carry electric charge and as a result they undergo only weak interactions, hence their experimental elusiveness: neutrinos may pass through ordinary matter almost unaffected. There is one neutrino “flavor” associated to each generation of elementary constituents. Understanding flavor from first principles remains a mystery, and it is a great challenge to find a natural explanation for both the origin as well as the values of the many free parameters that characterize the flavor sector. As unique and fundamental building blocks of the Standard Model neutrinos may hold important clues for what lies ahead. Given the success of the Standard Model and the gauge principle on which it is based, it is now widely believed that any extension of the Standard Model, even ones that incorporate gravity, should be based on a gauge principle of some sort. Unfortunately, it is hard to directly probe the beyond the Standard Model regime. The universe, on the other hand, is capable of accelerating particles to much higher energies than humans can, and are a great potential source of information. But the precise mechanism by which nature manages to create very highly energetic cosmic rays remains poorly understood. On the other side of the extreme, there is yet another theory which is remarkably successful, the standard model of cosmology. It describes several aspects of cosmology very well and recent results from the Planck satellite (see Figure 1) have yet again confirmed its predictions. It raises however at least as many questions as it answers. It assumes the existence of dark matter and dark energy, neither of which are part of the standard model. It assumes a period of inflation in the early universe which is also very difficult to reconcile with the standard model. And it assumes that the universe started out in a singular configuration, the famous big bang. A proper description of the big bang requires a theory which reconciles general relativity with quantum mechanics. String theory is a theory which does precisely that, and has provided a plethora of theoretical ideas over the past decades, but which remains extremely difficult to verify experimentally. Progress in all these fields will require great effort both on the theoretical as well as the experimental side. Precise astrophysical measurements, combined with earth based experimental data, must be developed side by side with theoretical ideas to further improve the understanding of the world we live in. Let us first mention some of the challenges facing particle physics today: