The present disclosure generally relates to semiconductor structures and, more particularly, to single fin structures and methods of manufacture. The structure includes: an active single fin structure; a plurality of dummy fin structures on opposing sides of the active single fin structure; source and drain regions formed on the active single fin structure and the dummy fin structures; recessed shallow trench isolation (STI) regions between the dummy fin structures and the active single fin structure and below a surface of the dummy fin structures; and contacts formed on the source and drain regions of the active single fin structure with a spacing of at least two dummy fin structures on opposing sides of the contacts.