The paper analyses the main terms and concepts using in contemporary English- and French-language historiography for describing informal ties acted along with official administrative practices in Europe during the Modern Time. The author shows different interpretations of concepts «fidelity relationships», patron-client networks, brokerage, clientelism, friendship. The meaning of the term «fidélité» / «fidelity» is characterized according to the views of R. Mousnier, his followers and opponents. The article considers the ideas of American historian Linda Levy Peck concerning such notions as «client», «clientage», «gift», «access», «allocation», «contract» as well as her theory of «court patronage» and «court brokers». To develop the problem of «brokerage» the paper gives an overview of Sharon Kettering’s main ideas about the system of interactions between patrons, brokers and clients in France in the 17th century. Attention is also focused on the practices of using the term «credit» / «credit of trust» by French- and English-language historians (A. Jouanna, K.B. Neuschel, Sh. Kettering). The examples of studies, devoted to French noble elite (authors - P. Gatulle, J. Duma), demonstrate the use of concepts «réseaux», «cercle», «nébuleuse». Finally, the author shows how the «political», «electoral», «land» and «urban» clienteles were investigated by C. Patterson, Sh. Kettering and others.