A hydrogen generator is formed of a strip of corrugated material that has been folded back and forth upon itself to define a monolith having multiple fluid flow regions. At least one of these regions is used for combustion, and at least one of these regions is used for steam reforming. Water is introduced into another fluid flow region, so as to receive heat from products of combustion, and to be converted into steam. The steam is directed into one or more regions used for steam reforming, so as to produce hydrogen for use in a fuel cell. In its more general form, the invention includes a compact heat exchanger, formed of a strip of corrugated material that has been folded back and forth upon itself, the heat exchanger being capable of transferring heat among three or more fluid streams.