most people think that the author of acts also wrote the gospel of luke, as acts 1:1 refers to 'the former treatise have i made, theophilus, of all that jesus began both to do and teach'. the traditional view is that both the two books were written "c." 60 by a companion of paul named luke. many theologians still think so. but some think the books were written by an unknown author at a later date, sometime between 80 and 150.