The Structure is the theoretical concept of a force throughout the heartland that promotes or represents its idea of order, harmony and structure.
It is unknown whether it actually exists. If it does, it may be the same force as the Shape, one may be responsible for the other, or they may be completely unrelated yet producing similar effects and monsters. Similarly, the Structure commonly appears in opposition to the Course.
Duvall is often associated with the Structure, as the bugs of the Sleeping City are organized and see the world in a way lining up with these concepts.