In Warhammer 40,000, there are many different types of warriors, ranging from the mighty Space Marines to the brutal Orks, the agile Eldar to the massive and dreaded Tyranid Warriors. To represent the abilities of these creatures in the game, there are nine categories that describe the various aspects of their physical and mental make-up. These are called Characteristics. All characteristics are measured on a scale of 0 to 10. The higher the value of a characteristic, the better it is, except for Saves. The characteristics are; Weapon Skill (WS), Ballistic Skill (BS). Strength (S), Toughness (T), Wounds (W), Initiative (I), Attacks (A). Leadership (Ld) and Save (Sv).

Defines how skilled a creature is with his weapons in close combat, or simply how determined and vicious a creature is. The higher the score, the more likely the warrior will land blows on a close combat opponent. A normal human has WS3. A battle-hardened Space Marine will have WS4 or even WS5.

Shows how accurate a creature is with ranged attacks, such as guns, rockets or energy weapons, It also includes a measure of the warrior's technical competence with his weapons and ammo supply. The higher this score is, the easier a creature finds it to hit when it shoots at something. Some monsters have natural weapons that can be used at range (they may be able to spit venom, for example) and their BS is used to determine whether they hit or not.

Shows how physically - strong a creature is. An exceptionally puny creature may have a Strength of 1, a deadly Tyranid Lictor has S6 and most humans have S3. Strength tells us how hard a creature can hit in close combat or how easily it can hurt an enemy.

This measures a creature's ability to resist physical damage and pain, and includes such factors as the toughness of its flesh, hide or skin. The tougher a creature, the better it can survive enemy blows or shots. A human is T3, a genetically-enhanced Space Marine is T4. Things with a Toughness of 6 or more are usually monstrous creatures with special rules to reflect their great size.

Shows how much damage a creature can take before it either dies or is so badly hurl it can't fight any more. Most humans/human-sized creatures have only a single Wound. Heroes and large monsters are often able to withstand several wounds that would slay a lesser creature, and so have a Wounds value of 2, 3, 4 or even more.

Indicates how alert a creature is and how quickly it reacts. Creatures with a low Initiative score are slow and cumbersome, creatures with a high Initiative score are much quicker and more agile. In close combat, faster creatures gain a big advantage over slower ones in that they strike first.

Indicates the number of Attacks a creature makes during close combat. Most creatures only attack once, although some warriors of exceptional skill or monsters can strike several times. The number of Attacks a creature makes may be increased if it has the added impetus of charging into its toe or is fighting using two weapons.

A creature with a high Leadership value is courageous, steadfast, and self-controlled. A creature with a low value is the opposite. Creatures with high Leadership can lead others, inspiring them on to greater feats of valour.

A creature's Saving throw gives it a chance of avoiding harm when it is struck or shot. Most creatures have a Saving throw based on what kind of armour they are wearing, so their Saving throw may be improved if they are equipped with better armour. Other creatures may receive a natural Saving throw from having a thick hide orchitinous shell.

Some creatures have been given a '0' for certain characteristics, which means that they have no ability whatsoever in that field. This usually applies to creatures unable to use missile weapons, and so they have a BS of 0. but it might equally apply to other characteristics too (eg, a defenceless model will have no Attacks whatsoever).

Sometimes, a unit may be called upon to make a Leadership test, most commonly to direct its fire or hold its ground. To take a Leadership test, roll 2D6 and compare the combined score to the unit's Leadership value. If the dice score equal to or under the Leadership value, the test is passed, if the dice score over the characteristic, the test is failed. Modifiers may apply to the Leadership characteristic in particularly trying circumstances, eg. -1 if the unit is below half its starting strength. Characteristic tests are used for other things, as detailed in the army's Codex book.

Each creature in Warhammer 40,000 has a profile that lists the value of its characteristics. In the Codex books, you will find profiles for many races and creatures. Below are the profiles for a Tyranid Termagant and an Imperial Space Marine.

As you can see, both are similar in some respects. They have the same Initiative value which means they are equally quick in close combat. Such creatures have 1 Wound and 1 Attack which is the norm for man-sized creatures. When it comes to BS and WS, S and T, however, the Space Marine is superior to the Termagant.
The Space Marine's Ballistic Skill of 4 and Weapon Skill of 4 mean the Space Marine will hit more often in shooting and close combat. The greater Strength value gives the Space Marine a better chance of injuring or killing the Termagant in hand-to-hand combat. Space Marines are extremely robust, with their high Toughness meaning they are better than ordinary humans in surviving damage inflicted on them. The Space Marine has a Leadership of 8, which is slightly higher than the average Leadership for most warriors. Termagants are animalistic, bioengineered predators which can be easily confused without the telepathic control of the larger hive organisms, and so have a low Leadership of 5. The Space Marine's thicker armour gives him another marked advantage over the Termagant, as any shot or blow that hits the Space Marine is deflected on a D6 roll of 3 or more. The Termagant needs a roll of 6 to be saved by its chitinous armour plates.
Obviously. Termagants are no match for Space Marines when fighting one to one but. as Termagants are usually found in large broods this can make them challenging opponents, even for Space Marines.

Generally, you'll find characteristic profiles come with one other piece of information - the points value per model. This represents the relative battlefield value ot the creature in question. Points values are an abstract calculation which take into account a huge number of different factors including characteristics, different races' overall strengths and weaknesses, basic weapons, unit size, rarity and so forth.
For comparison. Space Marines are worth 15 points, and Termagants 7. This means Space Marines can be outnumbered by Termagants by at least two to one and still have an even chance of winning.

Set in the far future, the Warhammer 40,000 universe is home to all sorts of tanks, war machines and other combat vehicles, both human built and alien. To reflect the many differences between creatures of flesh and blood and constructs of steel and iron, vehicles have many different rules and their own set of characteristics. Vehicle characteristics are described in more detail in the Vehicles section

A good commander does not need to take risks - he merely waits for his foe to do so