Finnish has a system of possessive suffixes.
There are five distinct suffixes, depending on the person that is acting as the possessor:
The suffixes have no distinction for the number of the possession(s), but can be attached to inflected forms; that is, words can be inflected even if they have a possessive suffix. The first-person singular possessive suffix has an alternative version, -in, which is poetic and thus chiefly used in poetry and music.
The suffix attaches to the end of the word, but assimilates a final -n in the genitive and illative forms. Note that there are no separate nominative forms for inflected words; both the nominative singular and plural have identical forms to the genitive singular, if a possessive suffix is present.
The first-person and second-person suffixes can be used to not just supplant, but also replace the pronoun, which can be omitted if a possessive suffix is present; thus taloni and minun taloni are synonymous. The third-person suffix however in many cases still requires the third-person pronoun (but not for instance with reflexive usage) or another corresponding pronoun and is not used if the headword in genitive is not a pronoun (such as if it is a name). In colloquial language, possessive suffixes are usually not used, with pronouns in genitive being the preferred option.
Most nouns can receive a possessive suffix. In addition, the comitative case requires a possessive suffix for nouns (but not adjectives).
Adjectives do usually not receive a possessive suffix, even when used with a noun that has a possessive suffix. Instead, if the adjective is used being substantively, i.e. without a modifying noun, it may receive a possessive suffix.
In addition, adjectives used for comparisons of equality (such as ikäinen ("of ... age, as old as"), pituinen ("of ... length, as long as") etc.) can receive a possessive suffix (such as ikäiseni ("of my age, the same age as me, as old as me")). In this case, the modified noun does not automatically receive a possessive suffix.
In some verb phrases, an object or some other word may receive a possessive suffix. There are two main types:
Agent participles require either a possessive suffix or a subject in genitive. For other types of participles, possessive suffixes are used as for adjectives.
Some verb forms, including participles, have special uses for possessive suffixes:
Certain postpositions, such as kanssa or luona, can also receive a possessive suffix. For some, such as mielestä, it is required when the complement is a personal pronoun; thus henkilön mielestä and jonkun mielestä, but hänen mielestään and (minun) mielestäni (however, in colloquial use, the suffix is often dropped here).
(Cardinal) numerals cannot receive a possessive suffix.