The top quark is the heaviest known elementary particle and the only quark that decays before hadronising, and thus gives direct access to its properties. With its large mass, it plays a crucial role for testing the predictions of the Standard Model (SM) and in the measurement of the Higgs boson properties. Top quark measurements also provide important input to QCD calculations. Moreover, various scenarios of physics beyond the SM expect the top quark to couple to new particles. The large data samples collected at the CERN LHC allow performing very precise measurements of top quark production and properties, challenging the accuracy of the state-of-the-art SM theoretical predictions, as well as measuring for the first time very rare SM proc...