Abstract: Data that represents chemical structures, and fragments thereof, are transformed into corresponding molecular keywords comprising letters and numbers that are associated with the original data representation. These molecular keywords encode the structural features of a given chemical structure. Molecular keywords are generated for linear structures, branching points, adjacent branching points, monocyclic, polycyclic and macrocyclic ring systems, stereo centers, ring-substituent patterns and molecular-formula atom counts. Indexing, database searching, and Web page presentation can be provided in conjunction with the molecular keywords representation.