The objective of study has been to define for every machining operation, a general methodology of optimum toot choice under its conditions. This leads to a two levels tool classification: machinong technique and operation. The methodology based on successive questions and criteria of divers natures, leads to choice specific parametric tool definition, rigorous of each operation type and to the basic equipments required of machining process (machine tool, part fixture, tool fixture). The automatic choice consist in matching definition parameters of an operation with tool caracteristic parameters. Some tool parameters are chosen from geometrical and technological matching tests. When archived, the choice integrate the tool service conditions. The cutting conditions identification method developed relies on linear programming. The methodology has been applied to external turning for the first level and to the cylindrical turning operation for the second level.