This book is a study of technological invention, looking beyond the stereotyped heroic inventors at the wider streams of change that led to various key technologies. The main case studies are flight, steam power and printing.
Lienhard discusses a lot around each of these topics, building a larger case about the nature of invention and technological change in general. On top of this, of course, there's also the stories of all the other people involved in the same technologies, who didn't quite make it, or improved things afterwards, and so forth.
His concluding discussion deals with the way education and the ideas about invention have changed, and suggests a thought-provoking thesis that the way we think about these now encourages further change. I'm not sure I completely agree with that, but it's an interesting idea.