The main features of scientific plagiarism are described. By the material of three “cases” from the initial period of formation of crowd psychology incorrect borrowings in the works of H. Fournial, G. Le Bon, B. Sidis are analysed. In particular, in H. Fournial's book several cases of text plagiarism from the work of S. Sighele, including the so-called hybrid form - a combination of fragments of foreign material with references to the source and without them - are identified. Based on the analysis of six publications chronologically preceding the debate on the scientific priority of 1895 and not mentioned by any of the parties, charges of G. Le Bon of plagiarism of his ideas against S. Sighele are recognized groundless. All of them, without exception, are available in earlier sources. The fact of plagiarism of N.K. Mikhailovsky's text and ideas in the first American publications of B. Sidis was unnoticed by the scientific community. The author of the article published in this issue of the journal considers it