  We present recent work undertaken by the Evolution and Seismic Tools Activity
(ESTA) team of the CoRoT Seismology Working Group. The new ESTA-Task 3 aims at
testing, comparing and optimising stellar evolution codes which include
microscopic diffusion of the chemical elements resulting from pressure,
temperature and concentration gradients. The results already obtained are
globally satisfactory, but some differences between the different numerical
tools appear that require further investigations.

Astrophysics