Farsi is the language most commonly spoken in Iran. It derives from Indo-Iranian language, and it is most commonly called Persian instead of Farsi, or Parsi by Western European and North American English language speakers.

Farsi as a language is separated into several periods of language evolution. Old Farsi or Old Persian was spoken from about 500-300 BCE. Middle Persian dates from about 300 BCE to 800 CE. Modern Persian has been spoken since about 800 CE.

Modern Farsi has influenced many other languages, particularly in the geographic area close to Iran. Ties to Farsi can be noted in Turkish and Azerbaijani, among others. As well, Farsi is clearly closely related to Hindi.

Farsi has six main vowels and twenty-three consonants, differing from English alphabets. Nouns as in modern English, lack gender. Farsi tends to structure sentences as subject, prepositional phase, object and lastly verb. This differs from the subject, verb, and object construction of English. Further, Farsi relies most on endings to change words, rather than prefixes. English uses numerous suffixes and prefixes to change meanings, tense, or a word from noun to verb or adjective.

Modern Farsi does show influence by others languages. Farsi may include words from French, English, Arabic and Turkish languages. Especially technical and scientific language can be considered on loan to Farsi.

Some words from Farsi have migrated to the English language. For example the words assassin, angel, lemon, and julep are all derived from Farsi. More Farsi words migrate into the English language particularly with the use of Fingilish, or Penglish. This is Farsi written with the Latin alphabet. It is commonly used in applications of the Internet, like emails and chats. As well, texting may be done in Penglish.

Farsi clearly influences Arabic since it was once the main language used in trade when the Persian world was preeminent. The Ottoman Empire used Farsi, as did many others. Persian literature, often written in Old or Middle Farsi is prized by many.

Some well-known examples of works written in Farsi include the Rubaiyat of Omar Khayyam and the beautiful and spiritual work of Rumi, which helped found the Sufi belief structure.