This chapter introduces a two-directional PCA/LDA approach that is a useful statistical technique applied to biometric authentication. We first describe both bi-directional PCA (BDPCA) and BDPCA plus LDA. Then, some basic models and definitions related to two-directional PCA/LDA approach are given. Next, we discuss two-directional PCA plus LDA. And, finally, the experimental results and chapter summary are given.