My chapter in Beautiful Code is titled Another Level of Indirection. In it I discuss how the filesystem code in the FreeBSD kernel employs various levels of indirection to structure the features it offers in a coherent way. In a related article, Abstraction and Variation, appearing in this month's IEEE Software Tools of the Trade column I explain how indirection is just one of the many mechanisms at our disposal for abstracting away non-essential complexity from the problem at hand.