A possible approach to representation theory is to consider representation theory of a group "G" as a harmonic analysis on the group "G" w.r.t. the two sided action of "G × G". Indeed, to know all the irreducible representations of "G" is equivalent to know the decomposition of the space of functions on "G" as a "G × G" representation. In this approach representation theory can be generalized by replacing the pair "(G × G, G)" by any spherical pair "(G,K)". Then we will be led to the question of harmonic analysis on the space "G/K" w.r.t. the action of "G".