Document Type: Special Issue of BIMS in Honor of Professor Freydoon Shahidi
In the spirit of the Langlands proposal on Beyond Endoscopy we discuss the explicit relation between the Langlands functorial transfers and automorphic $L$-functions. It is well-known that the poles of the $L$-functions have deep impact to the Langlands functoriality. Our discussion also includes the meaning of the central value of the tensor product $L$-functions in terms of the Langlands functoriality. This leads to the theory of the twisted automorphic descents for cuspidal automorphic representations of general classical groups.