Abstract: Regularization is a process that assigns meaningful values to divergent sums. In this talk, we will explore regularization in the context of automorphic forms and discuss 3 applications: (1) the Gan–Gross–Prasad (GGP) conjecture for Fourier-Jacobi period and Rankin-Selberg L-function for GL(n)xGL(n), (2) the rationality of L-functions, and (3) Faltings heights and subleading terms of adjoint L-functions.