Once you have located and read an adequate number of sources, incorporated ideas from your reading with your own understanding of the topic, and presented your analysis of your topic in a research paper, it is essential to cite the sources and you must use the proper bibliographic format to do so.
The main reason for citing your sources is to give credit to those authors whose ideas you used in your research. Even when you do not quote directly from another work, if reading that source contributed to the ideas presented in your paper, you must give the authors proper credit by including their work in your bibliography. Citing your sources allows readers of your work to easily find the sources to which you've referred.
If you do not cite the sources upon which your research is based, you will be guilty of plagiarism. Plagiarism is using the ideas and writings of others and representing them as your own. Even if you do not copy another source word-for-word, but rather rephrase the source without attributing it to the original author by including a citation, you are guilty of plagiarism. Plagiarism is a serious violation of academic standards and is punishable with a failing grade, possible expulsion from the institution, and may subject you to ostracism by your peers. The increasing availability of electronic information has unfortunately made it easy to copy another author's works.