Comparative mythology studies myths from multiple cultures to identify recurring structures, symbols, and functions. Scholars use cross-cultural parallels to trace the development of religions and societies, to reconstruct ancestral narratives, and to evaluate psychological interpretations of myth. Comparative catalogs map recurring motifs such as world-egg cosmogonies, flood cataclysms, dying-and-reborn deities, and creative sacrifice narratives across disparate regional traditions.

The field expanded during eighteenth and nineteenth century comparativism, though twentieth century researchers increasingly favored particularist critiques of sweeping generalizations, while contemporary work blends linguistic, historical, and structural approaches, including E. J. Michael Witzel's efforts to model successive layers of global mythic traditions.

Comparative cataloging shows that motifs span creation narratives, flood cataclysms, hero quests, dying-and-rising gods, trickster bargains, shapeshifting culture heroes, initiatory underworld descents, and cosmic animal hunts that encode social law, subsistence practices, and astronomical observation across continents, allowing researchers to trace how ritual economies and storytelling networks moved together.

Anthropologist C. Scott Littleton defined comparative mythology as "the systematic comparison of myths and mythic themes drawn from a wide variety of cultures". By comparing different cultures' mythologies, scholars try to identify underlying similarities and/or to reconstruct a "protomythology" from which those mythologies developed. To an extent, all theories about mythology follow a comparative approach—as scholar of religion Robert Segal notes, "by definition, all theorists seek similarities among myths". However, scholars of mythology can be roughly divided into particularists, who emphasize the differences between myths, and comparativists, who emphasize the similarities. Particularists tend to "maintain that the similarities deciphered by comparativists are vague and superficial", while comparativists tend to "contend that the differences etched by particularists are trivial and incidental".

Comparative approaches to mythology held great popularity among eighteenth- and nineteenth-century scholars. Many of these scholars believed that all myths showed signs of having evolved from a thought which interpreted nearly all myths as poetic descriptions of the sun's behavior. According to this theory, these poetic descriptions had become distorted over time into seemingly diverse stories about gods and heroes. However, modern-day scholars lean more toward particularism, feeling suspicious of broad statements about myths. A recent exception is the historical approach followed in E.J. Michael Witzel's reconstruction of many subsequent layers of older myths.^{[non-primary source needed]}

Comparative mythologists come from various fields, including folklore, literature, history, linguistics, and religious studies, and they have used a variety of methods to compare myths.

Some scholars look at the linguistic relationships between the myths of different cultures. For example, the similarities between the names of gods in different cultures. One particularly successful example of this approach is the study of Indo-European mythology. Scholars have found striking similarities between the mythological and religious terms used in different cultures of Europe and India. For example, the Greek sky-god Zeus Pater, the Roman sky-god Jupiter, and the Indian (Vedic) sky-god Dyauṣ Pitṛ have linguistically identical names.

This suggests that the Greeks, Romans, and Indians originated from a common ancestral culture, and that the names Zeus, Jupiter, Dyaus and the Germanic Tiu (cf. English Tues-day) evolved from an older name, *Dyēus ph₂ter, which referred to the sky-god or, to give an English cognate, the divine father in a Proto-Indo-European religion. An approach which is both historical and comparative was recently proposed by E.J. Michael Witzel. He compares collections of mythologies and reconstructs increasingly older levels, parallel to but not necessarily dependent on language families. The most prominent common feature is a storyline that extends from the creation of the world and of humans to their end. This feature is found in the northern mythologies of Eurasia and the Americas ("Laurasia") while it is missing in the southern mythologies of Subsaharan Africa, New Guinea and Australia ("Gondwanaland").