It is imperative the moment you know who you want your audience to be and what the purpose of your work to be, that you establish what genre correctly correlates to the two. Simply put, Genre is a category of literature or type of communication authors use when trying to reach out to their audience.
During my spring semester at CCNY we focused on 4 different types of Genres: A Memorandum, Technical Description, Lab Report, and Engineering Proposal. These 4 Genres all featured different intended audiences along with different rhetorical purposes for being written.