The Book of Five Rings, written by Miyamoto Musashi, a Samurai of legendary renown, about 1645 AD. It is a masterpiece of simple exposition written by a master swordsman, who, near the end of his spectacular life, tried earnestly to explain the essentials of individual combat and the essence of being a Samurai. His book is widely considered to a cornerstone of the philosophy of Bushido.
Hagakure - The Way of the Samurai, which means: "Hidden by Leaves", composed from dialogs by the famous Samurai, Yamamoto Tsunetomo, by a scribe, Tashiro Tsuramoto, about 1716 AD. It explains the major ideas and philosophy that are essential to the “way of the Samurai”, by which is meant the "way of dying". It contains numerous tales of various Samurai and their deeds which illustrate their philosophy and practice.
Bushido - The Soul of Japan by Inazo Nitobe which was first published 1899. It is an extremely literate presentation by a Japanese intellectual who wished to present Japan and its fundamental philosophy in a way that could be understood by Westerners. It describes how the Shinto Religion and Buddhism are the underpinnings of the essentially militaristic view of honor and life that are inherent in Bushido, the Samurai code.