In today's talk, we define the tautological $1$-form on the cotangent bundle and discuss some of its properties, such as the reproducing property, the universal property, naturality, etc. Next, we provide examples of some Lagrangian submanifolds of the cotangent bundle with the canonical symplectic form. Finally, we discuss some major open problems, like Eliashberg's cotangent bundle question: Are manifolds diffeomorphic if and only if their cotangent bundles are symplectomorphic?