We give an account of graphs of objects and total objects, where the objects are groups, groupoids, spaces and free crossed resolutions respectively. Graphs of groups were used by Higgins who defines the fundamental groupoid of a graph of groups and gives a normal form theorem. We give full details of this construction and illustrative examples. The new work generalises the notion of graphs of groups to graphs of groupoids, defines the fundamental groupoid of a graph of groupoids and gives a normal form theorem. We also implement the structure of graphs of groups and graphs of groupoids as the first two parts of a share package XRes in GAP4 to obtain normal forms computationally. Scott and Wall generalise graphs of groups to graphs of spaces and define a total space of a graph of spaces. We define analogous new constructions -the total groupoid of a graph of groups and the total crossed complex of a graph of free crossed resolutions. The total groupoid is isomorphic to the fundamental groupoid of a graph of groups. We also use a result of Scott and Wall on the asphericity of total spaces together with realisations of crossed complexes to give a result on the asphericity of total crossed complexes. We construct graphs of free crossed resolutions over graphs of groups to give free crossed resolutions of total groupoids. We conclude this work with applications of the total crossed complex of graphs of free crossed resolutions. We can use these free crossed resolutions to determine identities among relations a nd higher syzygies of finitely presented groups, obtained as vertex groups of total groupoids. We also extend presentations of free products with amalgamation and HNN-extensions obtained from reformulating the van Kampen theorem in terms of group presentations to give genera tings set for modules of identities among relations. We also give non-a belian extensions of groups using morphisms of free crossed resolutions to automorphism crossed modules. We conclude by relating our work to picture methods which are used to determine identities among relations.