The book "Fundamental Principles of the Metaphysics of Morals" was written by the famous German philosopher Immanuel Kant. It is a work of moral philosophy that explores the nature of morality, the principles that underlie it and the duties that individuals have towards one another.

In the book, Kant argues that moral principles are based on reason alone and are not dependent on particular circumstances or personal preferences. He believes that there are certain fundamental moral principles that are universally applicable, such as the principle of the dignity of all human beings.

Kant also introduces the concept of the "categorical imperative", which is a moral principle that is binding on all rational beings regardless of their individual desires or goals. He argues that this principle requires individuals to act in such a way that their actions could be made into a universal law without contradiction.

Overall, the book is a significant contribution to the field of moral philosophy and has had a profound impact on subsequent philosophical and ethical thought.