The absolute Galois group of Q, denoted Gal(\bar{Q}/Q) in the sequel, is a fundamental object in arithmetics since it carries a lot of informations about number fields. Unfortunately, it is nowadays not so well understood.
A classical way to study this group is to use p-adic numbers. Indeed, for each prime number p, the group Gal(\bar{Q_p}/Q_p) naturally embeds in Gal(\bar{Q}/Q) on the one hand, and can be more easily described on the other hand.
In this course, we will present two different aspects of the study of Gal(\bar{Q_p}/Q_p):
