The content of this book originates from 35 years of teaching “steam generators” to graduate students at the Politecnico of Milan, Milan, Italy, and from 45 years of professional activity in this area – rst in industry and then as founder of a design and consulting company. Beforediscussingthecontentof thetextbook,Iwouldliketopresenttherationale for the title. Boilers are machines consisting of steam-generating tubes only, that is, of internal and external tubes where water is transformed into saturated steam. Steam generators – or, simply, generators – indicate machines equipped with one or more of the following components: superheaters, reheaters, economizers, and air heaters – besides the steam-generating tubes that make up the boiler. Finally, those machines with tubes, where instead of water, a diathermic uid ows inside, are also called boilers, for their construction is similar to that of the latter. The above notwithstanding, the term “boiler” is used even when hot water or superheated water is produced instead of steam. Large systems designed to produce electricity have all components indicated above in addition to the boiler. In medium size systems, some of these components are always present, whereas in small ones a regenerator is frequently and approp- ately included. It is therefore justi ed to use “steam generators” as title, because it best matches the actual makeup of these systems.