  In this thesis, the quantum Hamilton Jacobi (QHJ) formalism is used to study
various exactly solvable (ES) and quasi -exactly solvable (QES) models. Using
this method, we obtain the bound state eigenvalues and the eigenfunctions for
the models studied. The central entity of this formalism in the logarithmic
derivative of the wave function, known as the quantum momentum function
(QMF).It is assumed that the point at infinity is an isolated singular
point.The kowledge of the singularity structure of the QMF is used to arrive at
the required solutions. We show that there are marked differences between the
singularity structures of the ES and QES models.
