Among indigenous religious systems, the names of certain deities and spirits recur frequently, especially among groups speaking related languages. Certain features of these traditional belief systems are broadly similar--for example, the existence of a supreme god identified with the sky and relatively remote from the everyday concerns of the people and addressed through spirits. Surface similarities notwithstanding, the configuration of the accepted roster of spirits, the rituals addressed to them, the social units (some based on the territorial community, others on common descent, generation, or sex) participating in specific rituals, and the nature and functions of religious specialists are peculiar to each ethnic group or subsection. Common to almost all indigenous systems is a range of spirits, some closely resembling in name and function the spirits recognized by neighboring Christians or Muslims.

Among the Oromo, especially those not fully Christianized, there is a belief in a supreme god called Waka, represented by spirits known as ayana. The ayana are mediators between the high god and human beings and are themselves approached through the kallu, a ritual specialist capable of being possessed by these spirits. The kallu is said to communicate directly with Waka and bless the community in his name. By contrast, some pastoral Oromo, such as the Guji and Borana, are regarded as monotheists.

Data as of 1991