It was in the summer of 1993 in Turkey, at the International Mathematical Olympiad, when a Bulgarian and a Romanian-American decided to write a book on problem-solving. This decision brought together two people separated by half of the world, not speaking each other's language and not knowing each other very well. Six months later they started working together in America.

We are Svetoslav Savchev, editor of the Bulgarian journal Matematika, and Titu Andreessen, former editor-in-chief of the journal Revista Matematică Timişoara and coach of the Romanian Mathematical Olympiad Team, now Director of the American Mathematics Competitions and head coach of the US Mathematical Olympiad Team.

The material we started with was vast, coming from all kinds of mathematical competitions, books, research papers, personal discussions and communications, and our own work. Such mathematical substance was sure to go beyond the pragmatic purposes of a traditional problem book. The most attractive pieces of mathematics refused to fit into the rigid schemes of an instruction manual, to merely exemplify typical problem solving techniques. Their depth and appeal endow such statements with individuality demanding a separate treatment. And our original program, in which they were destined to play an auxiliary role, impressed us increasingly as being too narrow.

Little by little, the idea came into being to isolate certain statements or groups of related statements into independent sections. By doing so we also hoped to emphasize the true source of their natural charm—the connection with authentic mathematical experience.