Audiobooks are usually distributed on CDs, cassette tapes, or digital formats (e.g., MP3 and Windows Media Audio). The term "books on tape" is frequently used as a synonym for audiobooks, but cassette tapes are no longer the dominant media for audiobooks. In 2005, Cassette-tape sales made up roughly 16% of the audiobook market, with CDs sales accounting for 74% of the market, and downloadable audio books accounting for approximately 9%. In the United States, the most recent sales survey (performed by the Audio Publishers' Association in the summer of 2006 for the year 2005) estimated the industry to be worth 871 million US dollars. Current industry estimates hover at around two billion US dollars per year. Most new popular titles put out by the major publishers are available in audio book format simultaneously with publication of the hardcover edition. There are approximately 25,000 current titles on cassette, CD, or downloadable format. Unabridged audiobooks are word for word readings of a book, while abridged audio books have text edited out by the abridger. Audiobooks also come as fully dramatized versions of the printed book, sometimes calling upon a complete cast, music, and sound effects. Each spring, the Audie Awards are given to the top nominees for performance and production in several genre categories. There are quite a few radio programs serializing books, sometimes read by the author or sometimes by an actor, most of them on the BBC.

Tracy Hogg who died from cancer on November 25 2004 aged 44, built a career as an expert in child-care and was nicknamed "the baby whisperer" for her ability to placate unruly infants. Although British, she made her name in the eclectic state of California, where she was hired as a maternity nurse and adviser by many Hollywood stars, among them Jodie Foster, Cindy Crawford, Jamie Lee Curtis and Calista Flockhart; even Arnold Schwarzenegger is said to have sought her counsel. The Yorkshire-born Dr Dolittle of the nursery always addressed her employers as "love" or "duck". It was a Hollywood producer who first referred to her as "the baby whisperer" - a reference to the book and film The Horse Whisperer, about a racehorse trainer with an uncanny ability to communicate with animals. She once said: "I've looked after so many thousands of babies, I can understand their language. And I teach new parents to understand their baby too. I also get babies on a routine, so that after three weeks they're sleeping through the night." Her fee for three weeks as a maternity nurse was more than ,000. If there was nothing particularly original about Tracy Hogg's approach to baby care, she had, according to her web site, "an uncanny ability to understand what babies need by listening to their cries and tuning in to their body language." This ability had probably been sharpened by earlier work she had undertaken with disabled children, who often lack verbal communication skills. Tracy Hogg was born to a large dairy-farming family near Doncaster, South Yorkshire, in August 1960. As a child she enjoyed accompanying her grandfather as he made his rounds at a local mental hospital, where he was head nurse. She attended the Doncaster School of Nursing. specialising in children with severe mental and physical disabilities. She underwent further training at Great Ormond Street, at the Children's Hospital in Leeds, and also did a stint with the World Health Organisation in India. At St Catherine's Hospital, Doncaster, she looked after children with learning difficulties. In 1992 she moved to America with her second husband, a car dealer, leaving her two young daughters from her first marriage in the care of their grandmother. This led some to question her parenting abilities, but Tracy Hogg wanted her children to continue their education in England, and the girls joined her during the holidays. Soon after arriving in Los Angeles, she was asked to help out a family with a new-born baby. The mother was Marilu Henner, who starred in the television sitcom Taxi. After that, reports of Tracy Hogg's skills spread by word of mouth. She went on to open a baby supplies store and set up an internet site, describing herself as "a British-trained nurse, lactation educator, and newborn consultant". In addition to working with individual clients, she organised classes for parents and trained child-care workers. In 1997 she produced an audio-tape for breast-feeding mothers which was designed to induce relaxation and reduce anxiety.