The introduction of your academic paper, regardless of the length, genre, or discipline in which you are writing, is your essential first impression. Recall that when you are reading others‘ work, the introduction is key to deciding how relevant the paper before you is for your own research. So this paragraph or section must be as well written as possible. With your introduction you wish to gain and keep your reader’s interest, announce both your research topic and your message, and give your reader a general idea of what to expect.
As the research paper can be conceived of as a building, I like this image of the entrance hall of the Empire State Building to show what elements your introduction must include.