Here's a short list of reasons you should cite:
--To avoid plagiarism
--To give credit where deserved
--To help your readers with their research
--To indicate that there is support for your argument or idea
What needs to be cited?
--Direct quotes, sentences, or phrases
--Paraphrases, which are summarized or re-phrased content
--Articles or studies that you refer to in your paper
--Historical or statistical facts
--Graphs, images, or charts
--Use of author's argument
What does not need to be cited?
--Proverbs and very well-known quotations
--Common knowledge. This may be difficult to determine. Think about facts that are common knowledge for a well-educated adult (you could even have a test subject). When in doubt, however, cite.
What about information I find on the web?
--You need to cite it unless it meets criteria above
What is plagiarism? A form of academic misconduct, either accidental or deliberate
What constitutes plagiarism?
--Using other's results or methods without permission and referencing
--Borrowing writing or words from any source, without proper referencing
More information on plagiarism can be found on the UI Libraries Guide on Copyright