It is recognized now that the international system of units will be redefined in terms of fundamental constants. Presently, the best estimate of fundamental constants values is given by a least square adjustment, carried out under the auspice of the Committee on Data for Science and Technology (CODATA) task group on fundamental constants. Among the fundamental constants, the fine-structure constant plays a particular role. It is a dimensionless constant therefore independent of the system of units. The fine-structure constant scales the electromagnetic interaction and can be measured in various fields of physics. Some of the experiments from which the fine-structure constant can be deduced will be reviewed, even if its present value is only determined by two experiments. The specific role of the fine-structure constant in the proposed new SI will be underlined.