The quark flavor sector of the Standard Model is a fertile ground to test any new physics effect through the Unitarity test of the Cabbibo-Kobayashi-Maskawa (CKM) matrix. 
Therefore, I present a lattice QCD calculation of the scalar and the vector form factors (over the full physical q^2 region including q^2=0) associated with the D to K meson semi-leptonic decay. 
The central CKM matrix element, V_{cs} in the Standard Model, is then calculated by comparing the lattice QCD results for the form factors and the experimental decay rate. 

In the second part of my talk, I present a lattice calculation of the pion electromagnetic form factor at up to q^2~6.0 GeV^2. 
This is a fundamentally important topic for our understanding of the hadron structure, the transition from perturbative to nonperturbative QCD, and to compare with JLAB experiment E12-06-101 
which proposes to extend the high quality pion form factor data to Q^2>6.0 GeV^2.