Simulating a String in 3d

Hi, How could one go about simulating a string in three dimensions? I''m not worried about the render so much as the math behind the movement of the string. I assume you would define a set number of points that represent the string, each being a 3d vector representation of a linear point of the string. But how could you move and end and make the string swing/wave properly? Any info would be appreciated, Ranger