In this thesis we exhibit an obstruction group for the following deformation theoretic problem. Given a diagram and a subdiagram of ringed topoi over a fixed ringed topos $\mathcal{S}$ and given a deformation $\xi$ of the

subdiagram, what is an obstruction group for finding a deformation of the diagram reducing to the given deformation $\xi$ of the subdiagram? We will calculate this obstruction group for a large variety of interesting cases as explicitly as possible. The results hold as well in the case of diagrams and subdiagrams of schemes over a fixed scheme $S$.