The idea for this book grew out of proposals at the APL86 conference in Manchester which led to the initiation of the I-APL (International APL) project, and through it to the availability of an interpreter which would bring the advantages of APL within the means of vast numbers of school children and their teachers. The motivation is that once school teachers have glimpsed the possibilities, there will be a place for an "ideas" book of short programs which will enable useful algorithms to be brought rapidly into classroom use, and perhaps even to be written and developed in front of the class. A scan of the contents will show how the conciseness of APL makes it possible to address a huge range of topics in a small number of pages. There is naturally a degree of idiosyncrasy in the choice of topics - the selection I have made reflects algorithms which have either proved useful in real work, or which have caught my imagination as candidates for demonstrating the value of APL as a mathematical notation. Where appropriate, notes on the programs are intended to show the naturalness with which APL deals with the mathematics concerned, and to estab­ lish that APL is not, as is often supposed, an unreadable language written in a bizarre character set.