Conversion to Digital Radio Broadcasting is well underway in the United States. The arrival has been accompanied by a series of technological and regulatory events. This book was written to provide a look at In-Band On-Channel (IBOC) technology from the inside, out. IBOC technology is also discussed in the context of its implementation by the company that brought it to market, iBiquity Digital Corporation (iBiquity). Receiver and transmission equipment manufacturers make and market numerous products licensed by iBiquity under the “HD RadioTM” brand name. At points in the book we thresh out the nature of the IBOC transmission protocol and its relation to products that bear the HD Radio trademark. The first two chapters provide a top-level view of the context of IBOC. Chapters 3 through 11 go into the nuts and bolts of the National Radio Systems Committee's NRSC-5 IBOC standard and how the technology works. The final portion of the book touches on other aspects of the technology.