Language forms similar to modern Finnish have been spoken in the current area of Finland and some neighboring areas for a long time, but it is unknown how long. The oldest written evidence is in a birch bark letter from the 13th century. These language forms are the origin of what are now regarded as Finnish, Estonian, Karelian, and some other languages, collectively known as Finnic (or Fennic or Balto-Fennic) languages. They have been heavily influenced by Baltic, Slavic, and Germanic languages, but mostly in vocabulary only. To some extent, and somewhat debatably, Germanic languages have also affected some features of grammatical structures.
The Finnish language, in the strict sense of the word, was created in the 16th century when a literary standard form was developed for a Bible translation and other religious purposes, based mostly in the language form spoken in the area of Turku (in southwest Finland). It was later developed by adapting features from other language forms (“dialects”), by adopting a more uniform orthography, and by extending the vocabulary in a planned manner especially in the 19th century, for use in administration, science, etc.
For centuries, religious use was the main context of using standard Finnish, as opposite to the local language forms, or “dialects”. Administration, education, etc. used Swedish, because Finland was part of Sweden (until 1808–1809). This was not changed by the annexation of Finland to Russia, though Russian was taken into use in some contexts in administration. However, later in the 19th century, there were many attempts at establishing a role for Finnish, the language of the majority of people, and it was increasingly used in literary form. In the 1860’s, a decision was made to give Finnish an official position along with Swedish.
The use of Finnish in official contexts as well as in literature and public communication increased, through some difficulties. The language had been just a spoken language in everyday use by mostly uneducated people, on one hand, and a standard language in limited use in the church and some other contexts, on the other hand. The language was developed by introducing a large number of words in all areas of life, often after systematic design. For example, Elias Lönnrot, the author of Kalevala, the national epos, also created a large number of Finnish terms for botany.
The standard variant of Finnish is known as yleiskieli (general/common language) or, especially in written form, as kirjakieli (book language) in Finnish. It has been taught at school, and it has been widely adopted. However, like most standard languages, it is really nobody’s native language. Radio, tv, and the Internet have made the common spoken language of the Helsinki area largely known and imitated in other areas, too, so we can say that in addition to standard literary Finnish and old local language forms, dialects, there is also a common “standard” spoken language. To many people, it is their most natural language, which they use in speech and often in informal writing, too, though they may switch to the standard literary variant in some contexts (like speaking to someone who does not seem to speak Finnish fluently).
From the late 20th century, the influence of English has been considerable especially in technology, science, humanities, and administration. The impact has mostly been limited to vocabulary and phrases.