The development of knowledge is never easy. One doesn't want to go over old ground again, but yet one needs to establish the new in the context of the old. One is also anxious about the novelty of the ideas are they new enough, or are they too 'way out' to be acceptable? In some fields perhaps these criteria are less important than in others. In education, I sense that 'novelty' is a tricky criterion, varying in value from society to society. In some societies the new ideas have to justify their adoption in the face to the old, tried and tested ideas. (Better the devil you know than the devil you don't!) In other societies the old ways have to justify their continuation in the face of the new, promising and exciting ideas. (I can't find a good proverb for this! Perhaps proverbs are all about preserving the past?) In any case, some people will argue, there is nothing new to be said about education anyway the problems are the same and it is only the context which changes. Mellin Olsen develops the reader's knowledge through this book in ways that are both novel and challenging. Their novelty is not in question, judging by reactions to them which vary from "they have nothing to do with mathematics education" to "they concern everything that is done in mathematics education".