Janus: A Summing Up is a book by Arthur Koestler, in which he develops his philosophical idea of Holarchies. The Holarchy provides a coherent way of organizing knowledge and nature all together. The idea behind the Holoarchy is that everything we can think of is composed by holons (Parts & Wholes together), and that each holon is located in such a way that it always has one above and one below. Every holon is like a two-faced Janus, the Roman god: one side (the whole) looks down; the other side (the part) looks up. In that way everything is organized, from the human body, to chemistry to the history of philosophy, etc.