This dictionary is the first compilation of all the elements of DNA sequences of known biological meaning. It lists alphabetically and describes some 700 nucleotide sequence ''words'' based on a four character alphabet (A,C,G,T) used to represent the hereditary information carried by DNA molecules. The data collected are scattered in more than 400 scientific papers. The dictionary is extremely useful for revealing and locating particular features of newly sequenced genome parts and for constructing artificial sequences. A context index, an index of all pentanucleotide derivates of the word entries, provides a quick way to ascertain whether a potentially interesting site encountered in a sequence has already been identified in a different context. Reference tables, such as restrictions, site tables, or oligonucleotide frequency distributions, are also included. This book is of interest to molecular biologists and genetic engineers.