Appears in collection : Summer School on the Langlands Program

This is an introduction to what is nowadays called the Relative Langlands Program whose rough aim is to enhance the original Langlands conjectures from group to certain G-spaces named spherical varieties. The development of this relative aspect of the Langlands program originates from the discovery, by way of many examples, that automorphic periods and local distinction problems are often related to functoriality and/or L-functions.