1 Subfields and scope
2 History
2.1 Early history
2.2 19th century
2.2.1 Foundational theories
2.3 20th century
2.3.1 Set theory and paradoxes
2.3.2 Symbolic logic
2.3.3 Beginnings of the other branches
3 Formal logical systems
3.1 First-order logic
3.2 Other classical logics
3.3 Nonclassical and modal logic
3.4 Algebraic logic
4 Set theory
5 Model theory
6 Recursion theory
6.1 Algorithmically unsolvable problems
7 Proof theory and constructive mathematics
8 Connections with computer science
9 Foundations of mathematics