The physical properties of the ionized layer in the Earth's upper atmosphere enable us to use it to support an increasing range of communications applications. This book presents a modern treatment of the physics and phenomena of the high latitude upper atmosphere and the morphology of radio propagation in the auroral and polar regions. Chapters cover the basics of radio propagation and the use of radio techniques in ionospheric studies. Many investigations of high latitude radio propagation have previously only been published in Conference Proceedings and organizational reports. This book includes many examples of the behavior of quiet and disturbed high latitude HF propagation. Ample cross-referencing, chapter summaries and reference lists make this book an invaluable aid for graduate students, ionospheric physicists and radio engineers.