The PiENu experiment aims at the most precise measurement
of the branching ratio B= (pi -> e nu )/ (pi -> mu nu).
This observable represents a very precise test of the
electroweak universality hypothesis and moreover, it is sensitive
to physics beyond the Standard Model.
The challenge of the experiment is to keep all the various systematic
errors under control for providing a high precision result.
After presenting the physics motivations, in my  talk I will focus on
the experimental techniques and on the results of the detector performances.