What is the difference between pietism and puritanism?

I would say "pietism" is simply the devotion to religious duties--of any religion; whereas, "puritanism" is an excessive observance of any religious doctrine, a strict observance of doctrine, and not necessarily meant only in relation to the separatists of the Anglican or Episcopalian churches often called "Puritans." The difference, then, could be just one of degree.

You could say that puritanism was a movement within the Calvinistic tradition, largely centered in England, and pietism was a resutant but more mystical movement within the Lutheran church, largely centered in the German states (including Prussia), with similar aims. You could also argue that the pietist movement, which looked upon the world as Satan's domain, was less likely to be involved with government than the puritan movement, which may have been true in Wuerttemberg but did not seem to be true in Prussia.

http://www.amazon.com/Piety-Politics-Absolutism-Wurttemberg-Cambridge/dp/0521256127

Or you could argue that, because of the similar aims, there was little difference between the two, with pietism being the continental counterpart of puritanism, an opinion expressed by no less of a major puritan figure than Cotton Mather.

http://books.google.com/books?id=YtHQakHBtf0C&pg=PA187&lpg=PA187&dq=puritanism+pietism&source=web&ots=I_H6OC6aXP&sig=upy7eGGXXf90io-pcrGc5zauc4U#PPA199,M1
(book "Max Weber: Critical Responses" by Bryan S. Turner, p. 199):

"Cotton Mather had recognized the close resemblance of these two Protestant movements, saying that 'ye American puritanism is so much of a piece with ye Frederician pietism' that they might be considered virtually identical."

Finally, the Columbia Encyclopedia says that the movements were similar but not identical, because the pietists intended to make the idea of Christian living predominant for believers, not to control the way that the rest of the world lived.

http://www.encyclopedia.com/doc/1E1-Pietism.html

"Although the movement bore resemblance to aspects of Puritanism, e.g., use of distinctive dress and the renunciation of worldly pleasures, the essential aim of the true Pietist was to place the spirit of Christian living above the letter of doctrine."

This appears to be a master's thesis question to fully answer ... or maybe even a book.