Keeping in view the importance of the above work and problems raised thereby, the present book embodies the investigations towards the study of various field associated with dyons (particle carrying simultaneously electric and magnetic charges) and gravito-dyons (particle carrying simultaneously gravitational or gravi-electric and Heavisidian or gravi-magnetic), the consistent analyticity of quaternion, generalization of Schwinger-Zwanziger dyon, Validity of Ehrenfest theorem and electromagnetic tensor for dyons and the physics beyond the standard model where the monopoles and dyons play an important role.