The term “hellology” can be found in the internet but does not seem to be attested in standard reference works. But never mind, I will use it here anyway in the sense of “the theory or study of hells.” Those of us new to Buddhism are often surprised/disappointed to know that Buddhism, too, has a concept of hell. Those of us who have been dealing with Buddhism for quite sometime either trivialize or banalize it away as a scare-mongering strategy or tactic of the Buddhists, or, rationalize it away somehow. Whether or not we like the idea of hell in Buddhism but we do have the idea of hell in Buddhism and hence we have to have a kind of “Buddhist hellology.” To begin with, Buddhist hellology would be a part of Buddhist cosmology (in the narrower sense of the “study or theory of the (external) world”). According to Buddhist sources, there are five or six kinds of worldly destiny/destination (or forms of existence) that a sentient being would land up. These fall into two sections: higher sphere of existence and lower sphere of existence. Importantly, neither are all higher spheres heavens or celestial realms nor are all lowers realms hell realms. Human realm belongs to the higher sphere but is still a human (though not always a humane) realm and not a celestial realm. Animal realms and realms of hungry ghosts belong to lower spheres but are not hell realms. Hell realms are the lowest in the domain of worldly existence. But there is not just one kind and level of hells. There are eighteen hellish realms. It will be imprecise to call hells in the Buddhist context as “Inferno” or “the infernal regions” because not hells are hot burning hells. There are cold hells too. Also the word “netherworld” would not suit our context because not all realms in the “netherworld” are hells. Importantly, there is neither the concept of “eternal damnation” nor of “eternal punishment.” No form of existence according to Buddhism is ever eternal (not even the deepest hell) and nobody can eternally punish anybody. But for pedagogical or didactic purpose, one might observe metaphors of punishment enacted during a theatrical performance. Pleasures or pains, which would be the consequences of one’s positive or negative attitudes and actions, are conceived of as being self-regulatory according to the karmic mechanism. Neutral attitude and actions, though possible, are karmically inconsequential. The depth of the hells and the intensity and duration of pain and suffering are obviously conceived of as being directly proportional to the gravity of the negativity of one’s karmic deed committed and accumulated. The most important cause for one’s birth in the hell realm is the deed committed and accumulated out of hatred, maliciousness, or malevolence. No bodhisattva would like to teach a sentient how to be born (karmically) in the hell, but if one insists he might tell us that the surest way to guarantee a place in the hell is to commit as much hatred- and maliciousness-motivated deeds as possible! There is also an interesting idea in Tantric Buddhism that there are only two destinations for a Mantric practitioner (like a snake in bamboo tube): one either attains Vajradharahood or takes birth in the hell. This hell is often called *vajranāraka (rdo rje dmyal ba). Although the Sanskrit source is not known to me, the Tibetan word can be found in some works in the bKa’ ’gyur and bsTan ’gyur. It is also used, for example, by gNubs-chen in his verses of epilogue of his bSam ta mig sgron (p. 503). The analogy of a snake in a bamboo pipe, I remember, has been used by A-ro Ye-shes-’byung-gnas in his Theg chen rnal ’byor la ’jug pa (Katja Thiesen’s Magister Thesis). It can also be found in what is known as the Jo bo’i gsung ’bum. See also the Bai ro’i rgyud ’bum (vol. 1, p. 288.5). The question is whether *vajranāraka is just another name for the lowest of the eighteen hells, or is it a separate hell, that is, one at the bottom of all hells. I think Tibetan scholars discuss this. What happens when our world dissolves? The hell habitats themselves will be dissolved but those hell inhabitants, who have not yet exhausted their karmic consequences, will be automatically be transferred to hells in other world systems. I thought Schmithausen has suggested, I do not remember where, that this problem of relocating hell inhabitants, who have not yet exhausted their karmic consequences, may have contributed to the development of Buddhist cosmology. Need to check! One last question: Do all Buddhist sources or systems really believe that such hells exist literally (and not just metaphorically)? What Śāntideva says might appeal to some modern rationality-inclined individuals, namely, that the damsels in the hell realms, who lure one to suffering, are actually nothing but projections of one’s unwholesome mind. But then is it also not said that our human realm, too, is just a projection of our mind? PS. (a) Si-tu-paṇ-chen in his bKa’ ’gyur dkar chag (p. 27) alludes to rdo rje khab rtse’i dmyal ba (according to the Kālacakra tradition), being the eighth hell. (b) See also Wangchuk 2009 (i.e. “A Relativity Theory of the Purity and Validity of Perception in Indo-Tibetan Buddhism”), where I also point out that, somewhat like what we find in John Milton’s poem, according to some Buddhist sources, too, one can make a heaven out of hell and hell out of heaven.