Abstract: This is a seminar about relative Langlands duality, a recent generalization of classical Langlands duality to the setting of spherical varieties and beyond. We will study basic topics in this theory, working towards an understanding of the paper of Sakellaridis--Venkatesh (and possibly Ben-Zvi--Sakellaridis--Venkatesh) dealing with global conjectures on automorphic periods and values of L-functions, as well as local versions of these conjectures which relate to the work of Gan--Gross--Prasad, Ichino--Ikeda and Lapid--Mao.