The text contains all the essential elements of communication principles, devices, circuits, antennas, and systems covering the electromagnetic spectrum from KHz to MHz of radio frequency (RF) that was developed in the formative stage of wireless technology. Also, the digital revolution, that has changed the landscape of modern electronics for wireless technology, has been discussed emphasizing the fundamentals including digital computers. The presentation of the book is in a concise yet complete way and stresses the physical and technical aspects with application viewpoints but using minimum possible mathematics. The book: Discusses the historical background of different developments of wireless technology from KHz to MHz and going through the GHz to THz in due perspective to provide a holistic view of the development of wireless technology from its inception to contemporary times. Contains in brief the basic concepts of electromagnetism like Maxwell’s wave equation, evanescent waves, surface waves, plasmonic waves that are used in wireless technology in some form or the other. Highlights the need for modulation and covers various modulation techniques such as continuous wave and pulse analogue modulation and modulation/demodulation systems that were developed in the formative stage of the development of wireless technology in the RF frequency range of KHz to MHz. Discusses the physical concepts and application view-points of active devices, RF transmission lines, antennas and systems used at KHz to MHz frequency domain of wireless technology. Covers the digital revolution that has changed the wholesale electronic systems of modern wireless technology, and the development of digital computers has also been discussed with a brief overview of laptops, supercomputers, and upcoming quantum computers. This overall scenario of historical perspective of wireless technology from KHz to THz and technical developments from KHz to MHz in the RF domain during the formative stage of development of wireless technology including fundamental developments related to digital revolution is expected to attract the interest of the entry level students, research scholars, professionals, and even the general readers alike with a new vision to have a quick yet in-depth glimpse of the progress of wireless technology since its inception till today. It is primarily written for junior undergraduate students in the fields of electrical engineering, electronics and communication engineering, wireless communication, telecommunication, and computer engineering. Research scholars and professionals can also refresh their idea of the developments of wireless technology during its formative stage and can get a flavour of the route to modern developments that have taken place henceforth.