> perhaps not a researcher, the best would be a grad student This reminds me of one of the other frequent failure points of having authors each write a chapter

> perhaps not a researcher, the best would be a grad student This reminds me of one of the other frequent failure points of having authors each write a chapter: they write a chapter that is really more of a survey paper about their favorite technique (maybe one they invented or have worked on). Usually that ends up with a choice of content and writing style that's a poor fit for a textbook. A grad student writing about something that is not their own research might be a way of avoiding that. I agree some kind of incentive is probably needed. It could be monetary, could be advancement-based, depends on the people writing and their situation. On the other hand, money might help for both: if there were grants for textbook writing, which e.g. a professor could use to buy out some of their own teaching and pay their summer salary, it'd also help out with the angle of "if I spend a year writing this book instead of journal articles, will I still get [tenure | full professor | etc.]?", because getting grant money is usually counted as a plus for advancement. There are some areas that have stronger internal incentives, mostly those in which there is significant controversy, and people have strong opinions about the Right Way to do something. The belief that existing books were doing it wrong and he could write one that introduced things correctly was what motivated Robert Harper to write his 2012 programming languages textbook, for example. Another variant of this is if there are no textbooks on a subject so far, and you feel it's as a result being overlooked: then writing a textbook can be a form of evangelism for your new field. There is less incentive to write a good textbook "for free" on established and uncontroversial subjects.