Religions commonly are taken to provide general orientation in leading one's life. We develop here the idea that religions also may have a much more concrete guidance function in providing systematic decision biases in the face of cognitive-control dilemmas. In particular, we assume that the selective reward that religious belief systems provide for rule-conforming behavior induces systematic biases in cognitive-control parameters that are functional in producing the wanted behavior. These biases serve as default values under uncertainty and affect performance in (...) any task that shares cognitive-control operations with the religiously motivated rule-conforming behavior the biases were originally developed for. Such biases therefore can be unraveled and objectified by means of rather simple tasks that are relatively well understood with regard to the cognitive mechanisms they draw on. (shrink)