  Almost 20 years after its discovery, the top quark is still an interesting
particle, undergoing precise investigation of its properties. For many years,
the Tevatron proton antiproton collider at Fermilab was the only place to study
top quarks in detail, while with the recent start of the LHC proton proton
collider a top quark factory has opened. An important ingredient for the full
understanding of the top quark is the combination of measurements from the
individual experiments. In particular, the Tevaton combinations of single
top-quark cross sections, the ttbar production cross section, the W helicity in
top-quark decays as well as the Tevatron and the world combination of the
top-quark mass are discussed.
