A code of length n and size M consist of a set of M vectors of n components. The components being taken from some alphabet set S. So a code C is a set of n-tuples subset of Sn. If S has a ring structure then C is called a linear code over S if it is an S-module. To every linear code C there corresponds its dual C⊥, if C C⊥, then C is called self-orthogonal. If C = C⊥ then C is called self-dual. In this thesis we will study linear and self-dual codes over the rings of four alphabets and in more details over the ring F2 x F2, this ring is isomorphic to the ring F2 + vF2 where v2 = v and F2 = {0; 1}. We would also study linear and self-dual codes for other rings in the form Fp + vFp for different primes p. Also we will construct simplex code over the ring F2 + vF2≃ F2 x F2
