Appears in collection : Reductive groups and automorphic forms. Dedicated to the French school of automorphic forms and in memory of Roger Godement.

We shall review the work of Z. Yun on zeta functions of orders, and of A. Altug on elliptic terms in the trace formula for GL(2). We shall then study the problem of Poisson summation for general linear groups. A suitable solution would be an important step in Langlands' proposed reformulation of the trace formula known as Beyond Endoscopy, which is aimed ultimately at the Principle of Functoriality.