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 D{\O}at Fermilab during {\RunI} from 1992 to 1996 and {\RunII} since 2001, are summarized. The combination of the published {\RunI} and preliminary {\RunII} results, taking correlated uncertainties properly into account, is presented. The resulting preliminary world average for the mass of the top quark is: $\MT=172.7\pm 2.9 \GeVc2$, where the total error consists of a statistical part of $1.7 \GeVc2$ and a systematic part of $2.4 \GeVc2$. Compared to the combination prepared for the LP 2005 conference, this combination for the EPS-HEP 2005 conference includes additional published {\RunI} and preliminary {\RunII} measurements.