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<p>Caltech has this available: <a href="http:&#x2F;&#x2F;authors.library.caltech.edu&#x2F;47756&#x2F;1&#x2F;FEYrmp48.pdf" rel="nofollow">http:&#x2F;&#x2F;authors.library.caltech.edu&#x2F;47756&#x2F;1&#x2F;FEYrmp48.pdf</a><p>There are some other good treatments too, although I can&#x27;t find them at the moment.