Citation is necessary because scholars (and other honest people) want to share ideas without stealing them.
When you create a research paper or presentation, it is (or should be) a combination of your original thoughts and the knowledge you have gained from the thoughts of others.
Citation is a way of giving credit to those whose ideas made your final product possible.
APA - Psychology, Social Sciences
MLA - English, Humanities
Chicago - History, Art
CSE - Biological Sciences, Medical Technology
ACS - Chemistry, Biochemistry
Not sure which style to use? Check with your professor or journal submission guidelines if submitting for publication .