The dialects of Finnish are divided into two distinct groups, the Western dialects and the Eastern dialects. The dialects are entirely mutually intelligible and distinguished from each other by only minor changes in vowels, diphthongs and rhythm. For the most part, the dialects operate on the same phonology, grammar and vocabulary. There are only marginal examples of sounds or grammatical constructions specific to some dialect and not found in standard Finnish. Two examples are the voiced dental fricative found in Rauma dialect and the Eastern exessive case.

There are two main varieties of Finnish used throughout the country. One is the “standard language” and the other is the “spoken language” . The standard language is used in formal situations like political speeches and newscasts. Its written form, the “book language, is used in nearly all written texts, not always excluding even the dialogue of common people in popular prose. The spoken language, on the other hand, is the main variety of Finnish used in popular TV and radio shows and at workplaces, and may be preferred to a dialect in personal communication.