Around 1864 Maxwell laid the foundation of electromagnetic theory, which formed the crowning achievement of nineteenth century physics. Max Born wondered how Maxwell could introduce the decisive step by adding the missing term 'the displacement current' without proper empirical foundation. At the beginning of the nineteenth century, it was realized that the basic principles of Maxwell need not undergo any change barring the concept of all-pervading ether. Till date the fundamental concepts of Maxwell remain the foundation of electromagnetism. After elaborating the basic concepts of Electromagnetic theory the text covers its extended regions discovers after World War II, describing the applications.