Warhammer Books: Codex Necrons

The Necron Codex describes a species of alien androids known as Necrons, who awaken after 60 million years of stasis to reclaim dominion over the galaxy they once ruled. The book contains the faction's deep and tragic history, details about their advanced technology, and rules for playing with a Necron army on the tabletop. 
The Necrons' origin and lore
The War in Heaven: The Necrons were once an organic race known as the Necrontyr, who lived short lives due to their star's harsh radiation. Desperate for immortality, they allied with the malevolent C'tan, or "Star Gods," to defeat their long-lived enemies, the Old Ones. They succeeded, but at an immense cost.
The Biotransference: Tricked by the C'tan, the Necrontyr underwent a process called biotransference, which transferred their consciousnesses into immortal, mechanical bodies of living metal (necrodermis), but stole their souls and emotions. Most Necrontyr became soulless drones, while the nobles retained some personality.
Overthrowing the C'tan: The Necron nobility, realizing the terrible price of their immortality, rebelled against their C'tan masters. Using powerful weapons developed by their Crypteks, they shattered the star gods into countless smaller "shards" and imprisoned them.
The Great Sleep: With the C'tan defeated but the psychically-active Aeldari becoming dominant, the Necrons entered a 60-million-year stasis on their Tomb Worlds, waiting for the galaxy to be ripe for their return.
The Great Awakening: The modern-day Necrons emerge to find a very different galaxy. Not all Tomb Worlds survived the long sleep, leading to various degrees of madness or corruption among the awakened Necron dynasties. 
Key Necron features
Dynasties: The Necron empire is divided into many dynasties, each with its own goals and methods. The codex provides detailed descriptions of prominent dynasties such as the Sautekh, Nihilakh, and Szarekhan.
Reanimation Protocols: A defining feature of the Necrons is their ability to self-repair. The "living metal" of their bodies can reassemble even catastrophic damage. On the tabletop, this is represented by the "Reanimation Protocols" rule.
Advanced Technology: Necrons possess unbelievably advanced technology, including Gauss weapons that disintegrate matter at a molecular level, and the use of the extradimensional Blackstone to create warp-dampening zones.
The Silent King: The original Necrontyr ruler, Szarekh, destroyed his command protocols and went into self-imposed exile after the biotransference. He has since returned to the galaxy with a new plan to combat the growing Tyranid threat using warp-dampening pylons. 
Additional book contents
Rules for Gameplay: The Necron Codex contains all the necessary rules for fielding a Necron army in games of Warhammer 40,000. This includes rules for units, wargear, and army-wide abilities.
Detachments and Detachment Rules (10th Edition):
The Awakened Dynasty: A versatile detachment focused on supporting leaders.
Canoptek Court: A detachment for armies heavy on Canoptek constructs and Crypteks, with rules centered around controlling sections of the battlefield.
Destroyer Cult: A detachment centered on the Destroyers.
Hypercrypt Legion: A highly mobile detachment that utilizes teleportation tactics to outmaneuver opponents.
Obeisance Phalanx: A detachment focused on elite units.
Crusade Rules: Special narrative-focused rules are included for players engaging in ongoing campaigns.