The paper introduces the π-calculus, a model of concurrent computation based on the concept of naming. It begins by presenting the simplest and original form of the π-calculus, followed by its generalization to polyadic form. The semantics are defined using both a reduction system and a version of labeled transitions called commitment. The paper also discusses the algebraic axiomatization of strong bisimilarity and provides a characterization in modal logic. The replication operator is analyzed, and the justification for the polyadic form is provided through the concepts of sort and sorting. Several illustrations of different sortings are given, including the presentation of data structures as processes that respect a particular sorting and the sorting for a translation of the λ-calculus into the π-calculus. The paper concludes with an extension of the π-calculus to ω-order processes and a brief account of Davide Sangiorgi's work on encoding higher-order processes at first-order.The paper introduces the π-calculus, a model of concurrent computation based on the concept of naming. It begins by presenting the simplest and original form of the π-calculus, followed by its generalization to polyadic form. The semantics are defined using both a reduction system and a version of labeled transitions called commitment. The paper also discusses the algebraic axiomatization of strong bisimilarity and provides a characterization in modal logic. The replication operator is analyzed, and the justification for the polyadic form is provided through the concepts of sort and sorting. Several illustrations of different sortings are given, including the presentation of data structures as processes that respect a particular sorting and the sorting for a translation of the λ-calculus into the π-calculus. The paper concludes with an extension of the π-calculus to ω-order processes and a brief account of Davide Sangiorgi's work on encoding higher-order processes at first-order.