  We construct supersymmetric unified models which automatically lead to a
period of inflation. The models all involve a U(1) symmetry which does not
belong to the MSSM. We consider three different types of models depending on
whether this extra U(1) is the subgroup of a non abelian gauge group, is a U(1)
factor belonging to the visible sector or is a U(1) factor belonging to the
hidden sector. Depending on the structure of the unified theory, on the
spontaneous symmetry breaking pattern and on whether we have global or local
supersymmetry, inflation may be driven by the non-vanishing vacuum expectation
value of a F-term or by that of a D-term. In both scenarios cosmic strings form
at the end of inflation, and they have different properties in each model. Both
inflation and cosmic strings contribute to the CMBR temperature anisotropies.
We show that the strings contribute to the $C_l$'s up to the level of 75 %.
Hence the contribution from strings to the CMBR and to the density
perturbations in the early Universe which lead to structure formation cannot be
neglected. We also discuss a very interesting class of models which involve a
$U(1)_{B-L}$ gauge symmetry.
