The problem of fusing beliefs in the Dempster-Shafer belief theory has attracted considerable attention over the last two decades. The classical Dempster's Rule has often been criticised, and many alternative rules for belief fusion have been proposed in the literature. We show that it is crucial to consider the nature of the situation to be modelled and to select the appropriate fusion operator as a function thereof. In this paper we present the cumulative and averaging fusion rules for belief functions, which represent generalisations of the subjective logic cumulative and averaging fusion operators for opinions respectively. The generalised operators are applicable to the combination of general basic belief assignments (bbas). These rules, which can be directly derived from classical statistical theory, produce results that correspond well with human intuition. Key words: Belief Theory, Subjective Logic, Fusion, Dempster's Rule