Bear Form is the second shapeshiftability learned by druids at level eight. Before level 40, it emulates mail armor and after that emulates plate armor. This form has tank-like abilities, similar to a warrior. Note that those with the Guardian specialization gain a 285% increase to armor.
While in bear form, the druid's mana bar is replaced by a rage bar. It is the most damage resistant form a druid has. While using [Frenzied Regeneration] and having enough Rage to fulfill the effect, this gives tremendous survivability.
As a druid, you really need to get a feel for when to change forms. Early on in the game, you may find it useful to cast a few long range spells, such as Wrath or Moonfire, then change to bear form when an enemy gets close.
Bear form is generally good to use against non-casters or those with higher armor, since you do higher melee damage, but at a slower attack speed.
If you're not sure if you can handle your (melee) enemy(s) (i.e. higher level, may be adds), use bear form until you get a feel for the fight.
In Bear Form, or as a Druid in general, you cannot block or parry, so your only method of ignoring damage is through dodging. However keep in mind that you do not gain rage from dodging an attack. However, druid tanks receive ways to absorb damage equal to or superior to blocking or parrying, and also have talents to make them gain rage when dodging.
The Bear Form ability was upgraded to Dire Bear Form at level 40. You received an increased armor bonus while in dire bear form, to match the introduction of plate armor to warriors and paladins at the same level. This form no longer exists, as of Patch 4.0.3.
The quest chain no longer exists. Previously, to gain the Bear Form ability you had to complete the Bear Form quest chain, starting with the quest Heeding the Call. Once completed, you needed to speak to the druid trainer that initially sent you on the quest, to learn the ability.
Patch 6.2.0 (23-Jun-2015): Bear Form now increases armor by 285% (up from 250%) for Guardian Druids.
Patch 6.0.2 (14-October-2014): Bear Form now increases armor by 250% for all Druid specializations (down from 330% for Guardian Druids, but up from 120% for non-Guardian Druids), no longer increases Haste and Critical Strike from items by 50%, but instead causes Haste to reduce the global cooldown, increases Stamina by 20% (down from 40%), and reduces magic damage taken by 10% (down from 25%).; For Guardian Druids, Bear Form now also reduces magical damage taken by 25%, reduces chance to be critically hit by 6%, and reduces chance for attacks to be parried by 3%.; Bear Form no longer increases Haste and Critical Strike from items by 50%, but instead causes Haste to reduce the global cooldown.
Patch 5.4.0 (10-Sep-2013) Bear Form now increases Stamina contribution from cloth and leather items by 40% (up from 20%).
Patch 4.3.0 (29-Nov-2011): Threat generated by classes in active tanking modes has been increased to 500% damage done, up from 300%.; Bear Form now provides an armor bonus of 120% at all levels, up from 65% for characters below level 40, making it easier for lower level druids to tank dungeons.; Bear Form now provides a Stamina bonus of 20%, up from 10%.
Patch 4.0.6 (8-Feb-2011): Entering or leaving a shapeshift no longer cancels root effects. It continues to cancel movement slowing effects. ; Druid forms now have an Archaeology Survey animation.