Copyright is concerned with more than properly crediting sources. Excessive use of another's original work, even if the source is properly acknowledged, may be a copyright infringement.

 Plagiarism is abuse of ideas and words from the work of someone else. Copyright is only concerned with original expression. Ideas and words alone cannot be copyrighted without originality.

 Copyright is addressed in both federal statutes and case law (legal decisions delivered by the courts). Except for some very specific statutes that apply to the results of scientific research for the government, plagiarism does not appear in federal statutes. However, it very well could be grounds for legal action, or in an academic environment, disciplinary action.