A hardcover or hardback (also known as hardbound, and sometimes as case-bound) book is one bound with rigid protective covers (typically of cardboard covered with buckram or other cloth, heavy paper, or occasionally leather). It has a flexible, sewn spine which allows the book to lie flat on a surface when opened. Following the ISBN sequence numbers, books of this type may be identified by the abbreviation Hbk.
Hardcover books are often printed on acid free paper, and they are much more durable than paperbacks, which have flexible, easily damaged paper covers. Hardcover books are marginally more costly to manufacture. Hardcovers are frequently protected by artistic dust jackets, but a "jacketless" alternative is becoming increasingly popular: these "paper over board" or "jacketless hardcover" bindings forgo the dust jacket in favor of printing the cover design directly onto the board binding.