The problem of plagiarism is one of the problems that are still found in the scientific and literary academic centers especially at students who are ignorant of scientific culture and culture of copyright. This book contains a comprehensive definition of the meaning of plagiarism, types, causes for it and also ways to avoid it. The practical side of the proposed system included detection of syntax and semantic plagiarism after it was handled by Pre-processing operations. the syntax plagiarism was detected by characters matching while the semantic plagiarism is done by taking the synonymous of the word with the aid of the WordNet program, as well as expand it by new words.