In this thesis we study the theta lifts of generic representations of the symplectic group and its double cover, the metaplectic group, defined over a local non-archimedean field F of characteristic 0. We consider the two basic problems regarding the local theta correspondence: first, determining when the lifts in question are non-zero, and secondly, explicitly describing those lifts. To obtain a full answer to the first question, we use Kudla’s filtration and a result of G. Muić on the irreducibility of standard modules of generic representation (the socalled Casselman-Shahidi conjecture). We also rely on the results on the lifts of tempered representations established by H. Atobe and W. T. Gan. Our answer to the second question includes an explicit description of all the non-zero lifts in terms of the Langlands classification. This part of our work is based on a detailed analysis of the possible subquotients of big theta lifts. Apart from the abovementioned results, we use the basic facts regarding the irreducibility of induced representations of the general linear group (established by A. Zelevinsky), as well as Muić’s results on the lifts of discrete series representations. Using the fact that theta correspondence in the stable range preserves unitarity (established by J.-S. Li), we arrive at an important consequence of our results: our description of theta lifts yields a method for constructing a large variety of unitary representations.