This book supplements information on ionosphere and the propagation of radio wave in and through the ionosphere particularly during the time of transient variations. The monograph is intended to help the advanced students to understand the theories, their applications and advancement in the field of wave propagation and operation of radio communication systems influenced by the ionosphere at prevalent tropospheric and upper atmospheric conditions. The book is appropriate for supervisors for teaching specific courses, for researchers to stimulate current topics, and for scientists working in the field of ionospheric physics for getting ready made information and future thought. It will also be profitable to the technicians involved in ionospheric and other related studies for designing equipments and techniques to be implemented thereafter. The book has glossary of terms, case studies and recent references. The references are up-to-date and they are separated chapter wise.