във

Usage notes
In writing, is used in front of words starting with ⟨в⟩ or ⟨ф⟩ and  is used elsewhere. In speech, and  are used interchangeably. In writing and in speech, във is also used as a stressed form of, even before words not beginning with ⟨в⟩ or ⟨ф⟩, as in

In verse, can also be used in front of words not starting with ⟨в⟩ or ⟨ф⟩ in order to maintain the syllable structure of the line.