The most common — and most obvious — use of the genitive case is to show possession. English has two ways to do this. One is through English's own genitive case endings (i.e., “–'s” or “–s'”). The other is with the preposition “of.” “The farmer's fields” means the same as “the fields of the farmer.”

Iter Marcī erat longum et difficile. (Mark's journey was long and difficult.)

Like most modifiers in Latin, words in the genitive case tend to follow the nouns they modify.

The Latin words meus (“my”), tuus (“your”), noster (“our”), vester (“your”), suus (“his, her, its, their”) are possessive adjectives. They already have the idea of possession in their meanings, and being adjectives, they must agree in gender, case, and number with the noun they modify; for example, canis meus (my dog), canēs meī (my dogs).