Various approaches for plagiarism detection exist. All are based on more or less sophisticated text analysis methods such as string matching, fingerprinting or style comparison. In this paper a new approach called Citation-based Plagiarism Detection is evaluated using a doctoral thesis [8], in which a volunteer crowd-sourcing project called GuttenPlag [1] identified substantial amounts of plagiarism through careful manual inspection. This new approach is able to identify similar and plagiarized documents based on the citations used in the text. It is shown that citation-based plagiarism detection performs significantly better than text-based procedures in identifying strong paraphrasing, translation and some idea plagiarism. Detection rates can be improved by combining citation-based with text-based plagiarism detection. Categories and Subject Descriptors H.3.3 [Clustering]: INFORMATION STORAGE AND RETRIEVAL – Information Search and Retrieval. General Terms Algorithms, Experimentati...