The Theoretical Particle Physics group studies the smallest constituents of matter and how these interact with each other. When particles are brought to collide at high energies, e.g. at the LHC accelerator at CERN, strong interactions dominate. These are described by a theory called QCD, which is formulated in terms of mathematical equations too complex to be solved exactly. Instead approximate but very sophisticated and detailed computer simulations of the collision process are developed in our group. These so-called Lund Monte Carlos are used all over the World to interpret experimental results. Complementary information is obtained by precision measurements at lower energies, e.g. in decays, and we actively develop theoretical descriptions of this. QCD is part of a bigger theory, the Standard Model. While immensely successful, it has its limitations and flaws, and therefore models are developed that attempt to go beyond it. The group is involved also in such studies.