The historical origins and current interpretation of the molecular chaperone concept are presented, with the emphasis on the distinction between folding chaperones and assembly chaperones. Definitions of some basic terms in this field are offered and misconceptions pointed out. Two examples of assembly chaperone are discussed in more detail: the role of numerous histone chaperones in fundamental nuclear processes and the co-operation of assembly chaperones with folding chaperones in the production of the world's most important enzyme.