Before a researcher can develop his or her own research question, it is important to find out what is already known about a given topic. This process is called a Literature Review. Completing a Literature Review prevents doing research that has already been done (or attempting to prove something that has previously been resolved). It also allows the researcher to fully understand where the subject is currently, what research has come before, and what still remains to be understood. Only when this has been completed should a researcher begin to conduct his or her own research.
Watch this short video for more information about writing a Literature Review