The inauguration of radio-telephone broadcasting has quickly aroused an enormous general interest in radio reception of speech and music. The possibilities of this new method of broadcasting information of general interest and entertainment can hardly be estimated. The method is revolutionary and has been aptly compared to the invention of the printing press in this respect. Vacuum tubes make possible the reception of radio-telephone speech and music and radio-telegraph signals with a degree of satisfaction not approached by prior devices. The vacuum tube appears to the layman as a complicated form of incandescent electric lamp which operates in a very mysterious manner. In writing this little book the author has endeavored to overcome this impression and to clearly set forth the elementary principles of theory and operation. It is assumed that the 'reader has no knowledge of radio and very little, if any, of electricity. Mathematics has been especially avoided in the treatment of the subject and no technical terms are used without their meaning being made clear.