Having 13 chapters in total, each of which is devoted to one aspect of warfare, The Art of War is an all-time classic Chinese military treatise written by Sun Tzu in the 6th century BC.

Summaries of each chapter:

1. Laying Plans/The Calculations: Explores the five fundamental factors (and seven elements) that define a successful outcome (the Way, seasons, terrain, leadership, and management). By thinking, assessing and comparing these points you can calculate a victory, deviation from them will ensure failure. Remember that war is a very grave matter of state.

All warfare is based on deception.

Hence, when able to attack, we must seem unable; when using our forces, we must seem inactive; when we are near, we must make the enemy believe we are far away; when far away, we must make him believe we are near.

2. Waging War/The Challenge: Explains how to understand the economy of war and how success requires making the winning play, which in turn, requires limiting the cost of competition and conflict.

... a wise general makes a point of foraging on the enemy. One cartload of the enemy's provisions is equivalent to twenty of one's own, and likewise a single picul of his provender is equivalent to twenty from one's own store.

3. Attack by Stratagem/The Plan of Attack: Defines the source of strength as unity, not size, and the five ingredients that you need to succeed in any war. In order of importance attack: Strategy, Alliances, Army, lastly Cities.
... the skillful leader subdues the enemy's troops without any fighting; he captures their cities without laying siege to them; he overthrows their kingdom without lengthy operations in the field.

There are three ways in which a ruler can bring misfortune upon his army:

A. By commanding the army to advance or to retreat, being ignorant of the fact that it cannot obey. This is called hobbling the army.

B. By attempting to govern an army in the same way as he administers a kingdom, being ignorant of the conditions which obtain in an army. This causes restlessness in the soldier's minds.

C. By employing the officers of his army without discrimination, through ignorance of the military principle of adaptation to circumstances. This shakes the confidence of the soldiers.

There are five essentials for victory:
(1) He will win who knows when to fight and when not to fight.
(2) He will win who knows how to handle both superior and inferior forces.
(3) He will win whose army is animated by the same spirit throughout all its ranks.
(4) He will win who, prepared himself, waits to take the enemy unprepared.
(5) He will win who has military capacity and is not interfered with by the sovereign.

4. Tactical Dispositions/Positioning: Explains the importance of defending existing positions until you can advance them and how you must recognize opportunities, not try to create them.

In respect of military method, we have, firstly, Measurement; secondly, Estimation of quantity; thirdly, Calculation; fourthly, Balancing of chances; fifthly, Victory.

5. Energy/Directing: Explains the use of creativity and timing in building your momentum.
There are not more than five musical notes, yet the combinations of these five give rise to more melodies than can ever be heard.
There are not more than five primary colors (blue, yellow, red, white, and black), yet in combination they produce more hues than can ever been seen.
There are not more than five cardinal tastes (sour, acrid, salt, sweet, bitter), yet combinations of them yield more flavors than can ever be tasted.

In battle, there are not more than two methods of attack--the direct and the indirect; yet these two in combination give rise to an endless series of maneuvers.
The direct and the indirect lead on to each other in turn. It is like moving in a circle--you never come to an end. Who can exhaust the possibilities of their combination?

6. Weak Points & Strong/Illusion and Reality: Explains how your opportunities come from the openings in the environment caused by the relative weakness of your enemy in a given area.
If we wish to fight, the enemy can be forced to an engagement even though he be sheltered behind a high rampart and a deep ditch. All we need do is attack some other place that he will be obliged to relieve.
If we do not wish to fight, we can prevent the enemy from engaging us even though the lines of our encampment be merely traced out on the ground. All we need do is to throw something odd and unaccountable in his way.
By discovering the enemy's dispositions and remaining invisible ourselves, we can keep our forces concentrated, while the enemy's must be divided.

7. Maneuvering/Engaging The Force: Explains the dangers of direct conflict and how to win those confrontations when they are forced upon you.
In war, practice dissimulation, and you will succeed.
We may take it then that an army without its baggage-train is lost; without provisions it is lost; without bases of supply it is lost.
The Book of Army Management says: On the field of battle, the spoken word does not carry far enough: hence the institution of gongs and drums. Nor can ordinary objects be seen clearly enough: hence the institution of banners and flags.

In night-fighting, then, make much use of signal-fires and drums, and in fighting by day, of flags and banners, as a means of influencing the ears and eyes of your army.
Now a soldier's spirit is keenest in the morning; by noonday it has begun to flag; and in the evening, his mind is bent only on returning to camp.

8. Variation in Tactics/The Nine Variations: Focuses on the need for flexibility in your responses. It explains how to respond to shifting circumstances successfully.

There are five dangerous faults which may affect a general:
(1) Recklessness, which leads to destruction;
(2) cowardice, which leads to capture;
(3) a hasty temper, which can be provoked by insults;
(4) a delicacy of honor which is sensitive to shame;
(5) over-solicitude for his men, which exposes him to worry and trouble.

9. The Army on the March/Moving The Force: Describes the different situations inf them.
Camp in high places, facing the sun. Do not climb heights in order to fight. So much for mountain warfare.
Country in which there are precipitous cliffs with torrents running between, deep natural hollows, confined places, tangled thickets, quagmires and crevasses, should be left with all possible speed and not approached.
All armies prefer high ground to low and sunny places to dark.
The rising of birds in their flight is the sign of an ambuscade. Startled beasts indicate that a sudden attack is coming.

...soldiers must be treated in the first instance with humanity, but kept under control by means of iron discipline. This is a certain road to victory.

10. The Terrain
We may distinguish six kinds of terrain:
(1) Accessible ground;
(2) entangling ground;
(3) temporizing ground;
(4) narrow passes;
(5) precipitous heights;
(6) positions at a great distance from the enemy.

11. The Nine Situations
The nine varieties of ground:
(1) Dispersive ground;
(2) facile ground;
(3) contentious ground;
(4) open ground;
(5) ground of intersecting highways;
(6) serious ground;
(7) difficult ground;
(8) hemmed-in ground;
(9) desperate ground.

...the skillful general conducts his army just as though he were leading a single man, willy-nilly, by the hand.

On the day that you take up your command, block the frontier passes, destroy the official tallies, and stop the passage of all emissaries.

Be stern in the council-chamber, so that you may control the situation.

12. The Attack by Fire/Fiery Attack: Explains the use of weapons generally and the use of the environment as a weapon specifically. It examines the five targets for attack, the five types of environmental attack, and the appropriate responses to such attack.

The five ways of attacking with fire:
(1) burn soldiers in their camp;
(2) burn stores;
(3) burn baggage trains;
(4) burn arsenals and magazines;
(5) hurl dropping fire amongst the enemy.

13. The Use of Spies/The Use of Intelligence: Focuses on the importance of developing good information sources, specifically the five types of sources and how to manage them.

Five classes of using spies:
(1) Local spies;
(2) inward spies - making use of officials of the enemy;
(3) converted spies - getting hold of the enemy's spies and using them for our own purposes.;
(4) doomed spies - doing certain things openly for purposes of deception, and allowing our spies to know of them and report them to the enemy.; (5) surviving spies - those who bring back news from the enemy's camp.

When these five kinds of spy are all at work, none can discover the secret system. This is called "divine manipulation of the threads." It is the sovereign's most precious faculty.

[From the Great Books  Series. Also see The Success Manual  - Encyclopedia of Advice, which contains summaries of 100+ Most useful books.]