+Proof theory is a branch of [Mathematical Logic](/wiki/mathematical_logic) that studies proofs as formal mathematical objects. It explores their structure, validity, and the properties of [Formal Systems](/wiki/formal_system) in which they reside.
+## See also
+- [Model Theory](/wiki/model_theory)
+- [Set Theory](/wiki/set_theory)
+- [Metamathematics](/wiki/metamathematics)