On the pion decay constant

The pion decay constant fπ plays a crucial role in many areas of low energy particle physics. Its value may e.g. be deduced from experimental data on leptonic pion decays. Here, we provide comments on several aspects of this evaluation. In particular, we point out that at the present level of experimental accuracy, the value of fπ is sensitive to the value of the pion mass chosen in its chiral expansion.