Treballs Finals de Grau de Matemàtiques, Facultat de Matemàtiques, Universitat de Barcelona, Any: 2017, Director: Albert Mas Blesa[en] The main goal of this work is to provide techniques for finding self-adjoint extensions to unbounded operators, widely used in Quantum Physics. For that we use and study the Cayley method, concluding in the existance of a bijection between self-adjoint extensions and isometries between the deficiency subspaces of the Cayley transform. Using this knowledge we briefly parameterise the 1D, 2D and nD cases with possible self-adjoint extensions, and after introducing Sobolev spaces, we perform in more detail the search of self-adjoint extensions of the hamiltonian and laplacian operators.