The authors outline homotopy theory and its application to field theory. They describe topologically non-trivial field configurations occurring in the Abelian Higgs model, CPN models, O(N) sigma models and in Yang-Mills gauge theories both with a Higgs sector (monopoles) and without one (instantons). Parameter quantisation via topology is also discussed for the cases of QCD3 and the Wess-Zumino effective action.