Any subset C of the group Znq is called a q-ary code of length n. For any element c 2 C, the weight of c, i.e. the number of non-zero entries of c, is denoted by wt(c). The Hamming distance of any two elements c1; c2 2 C is de ned to be dist(c1; c2) = wt(c1-c2). Also the minimum hamming distance of a code C is de ned to be the largest integer d such that for any c1; c2 2 C, we have dist(c1; c2)  d. The maximum size of any q-ary code of length n with minimum Hamming distance d is denoted by Aq(n; d). It this talk, we will provide an overview of a technique which employs representation theory of nite groups as well as some graph theoretical techniques to obtain some upper bounds for A2(n; d).