In this paper, we discuss an approach which determines the residues of certain families of Eisenstein series in terms of periods on the cuspidal data. By contrast, the traditional approach is to determine the residues of Eisenstein series in terms of certain L-functions attached to the cuspidal data. The relation between these two methods is the general conjecture which relates periods on the cuspidal data to the existence of poles or the special values of L-functions attached to the cuspidal data.