A finite graph Γ is said to be G-symmetric if G is a group of automorphisms of Γ acting transitively on the ordered pairs of adjacent vertices of Γ. In most cases, the group G acts imprimitively on the vertices of Γ, that is, the vertex set of Γ admits a nontrivial G-invariant partition B. The purpose of this thesis is to study such graphs, called imprimitive G-symmetric graphs. In the first pa...