If you are approached by an aggressive bear avoid direct eye contact, speak in a soft, calm voice and slowly back away from the bear. These actions often will help appease the bear.  The bear may slap the ground, huff, blow, and chomp its teeth or make a bluff charge to let you know it feels threatened and wants space. Do not run or turn your back to the bear.  Bears can outrun, out-swim and out-climb you. 

Make yourself appear bigger by raising your arms above your head, and continue to speak in a soft, calm voice and back away from the bear. 

If you are actually charged and attacked, fight back rather than "play dead." Capsaicin, or concentrated red pepper spray, has been a useful repellent when sprayed directly into the face of the bear, but it is only effective at close range and for threatening encounters.  Spray range is typically less than 30 feet.  Do not use capsaicin spray on objects or plants as a bear repellent, it may actually attract bears.

Kick, punch, and hit the bear with your fists, feet, and whatever weapon might be available.  Concentrate your attack on the bear’s face, eyes, and nose.

Get prompt medical treatment.  Notify your state wildlife agency to report the attack and have the bear captured and tested for diseases.