Combination of CDF and D0 Results on the Top-Quark Mass

The results on the measurements of the top-quark mass, based on the data collected by the Tevatron experiments CDF and DO at Fermilab during Run I from 1992 to 1996, are summarized. The combination of the published results, taking correlated uncertainties properly into account, is presented. The resulting world average for the mass of the top quark is: $M_t = 178.0 \pm 4.3 GeV/c^2$, where the total error of consists of a statistical part of $2.7 GeV/c^2$ and a systematic part of $3.3 GeV/c^2$.