The present work of our book is devoted to the study of common fixed points for single and multivalued mappings in nonlinear analysis. In the present work we obtain some common fixed point theorems in some of recently defined metric structures, like: cone metric spaces, fuzzy metric spaces, non-Archimedean PM-spaces and complex valued metric spaces by using different contractive conditions.The book ends with common fixed point of mappings satisfying rational inequality in complex valued metric spaces.