My fiance is coming to the us to get married on her tourist visa. When should we start filing for citizenship?

Aftercmarriage your fiancé will first need to become a lawful permanent resident. There is no direct path to citizenship based upon marriage to a United States citizen. While you and your fiancé may marry during her trip to the United States, she cannot use a tourist visa to enter the country with the intent to seek permanent residence. Such conduct can lead to serious repercussions including s permanent bar to admission. After you marry, you can start the immigrant visa process but you spouse should depart the country in compliance with her authorized stay. If you do not want her to leave after marriage then she should enter on a fiancé visa. This visa allows her to enter the country for the purpose of marrying and seeking permanent residence. You can read more about fiancé visas at http://myattorneyusa.com/k-1-and-k-2-visas-for-fiancees-and-derivatives.