If you've ever wondered why agile or lean development techniques work, The Principles of Product Development Flow: Second Generation Lean Product Development by Donald G. Reinertsen is the book for you. It's quite simply the most advanced product development book you can buy.
For those who hunger for a rigorous approach to managing product development, Donald Reinertsen's book is epic. Myths are busted on practically every page, even myths that are associated with lean/agile. For example, take the lean dictum of working in small batches. I push this technique quite often, because traditional product development tends to work in batches that are much too large. Yet it's not correct to say that batch sizes should be as small as possible. Reinertsen explains how to calculate the optimal batch size from an economic point of view, math and all. It's wonderful to have an author take these sorts of questions seriously, instead of issuing yet another polemic.
The book is structured as a series of principles, logically laid out and briefly discussed - 175 in all. It moves at a rapid clip, each argument backed up with the relevant math and equations: marginal profit, Little's law, Markov processes, probability theory, you name it. This is not for the faint of heart.
The use of economic theory to justify decisions is a recurring theme of the book. Its goal is to help us recognize that every artifact of our product development process is really just a proxy variable. Everything: schedules, efficiency, throughput, even quality. In order to trade them off against each other, we have to convert their impact into economic terms. They are all proxies for our real goal, maximizing an economic variable like profit or revenue. Therefore, in order to maximize the true productivity (aka profitability) of our development efforts, we need to understand the relationships between these proxy variables.