This article might be one of the best intros: Space-Time Approach to Non-Relativistic Quantum Mechanics R. P. Feynman Rev. Mod. Phys. 20, 367 – Published 1 April 1948

Caltech has this available: http://authors.library.caltech.edu/47756/1/FEYrmp48.pdf

There are some other good treatments too, although I can't find them at the moment.