This paper presents a way of classifying different forms of naturalness and unnaturalness. Three main forms of (un)naturalness are found as the following: history- based (un)naturalness, property-based (un)naturalness and relation-based (un)naturalness. Numerous subforms (and some subforms of the subforms) of each are presented. The subforms differ with respect to the entities that are found (un)natural, with respect to their all-inclusiveness, and whether (un)naturalness is seen as all-or-nothing affair, or a continuous gradient. This kind of conceptual analysis is needed, first, because (...) discussion concerning (un)naturalness is common in current bioethics and environmental ethics, and second, because the terms natural and unnatural are highly ambiguous. Thus, the lack of an exact definition of the type of (un)naturalness may lead into equivocation, other forms of bad argumentation, or at least vagueness. (shrink)