http://www.usembassy.org.uk/cons_web/faqs/iv/faq_spouse.htmCan I travel to the United States while my application for an immigrant or fiancé(e) visa is being processed?If you intend taking up permanent residence in the U.S., you are required to wait until the immigrant or fiancé(e) visa is issued. You cannot reside in the U.S. on a tourist visa or visa free under the Visa Waiver Program while waiting the issuance of an immigrant or fiancé(e) visa. However, if you wish to make a temporary visit at the end of which you will return to your permanent residence outside the United States, you may travel on a tourist (B-2) visa, or visa free under the Visa Waiver Program, if qualified.
If applying for a B-2 visa, you are required to furnish evidence of your residence outside the United States to which you intend returning at the end of your temporary stay. Although a pending immigrant or fiancé(e) visa application is not necessarily conclusive evidence of intent to abandon a U.K. residence, it is a factor considered by consular officers reviewing a visa application. If you are unable to convince the consular officer reviewing the application that you do not intend abandoning your residence, you will not be issued a visa.
When traveling to the U.S. either with a visa or visa free under the Visa Waiver Program, you should be sure to carry with you for presentation to an immigration inspector evidence of your residence outside the U.S. If the immigration inspector is not convinced that you are a bona fide visitor for pleasure, you will be denied entry into the United States.
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My fiancee and I are also in the middle of the I-129F process. I might have a new job soon that will not allow me to take a holiday to England at Christmas as originally planned so he will come here. We are under the understanding that as long as he does not have the visa in his passport, he can travel here as a regular tourist with provided documentation that he will be returning to his home in England {in his case- a round trip plane ticket, letter from his parents where he is residing and a letter from his job acknowledging his holiday and confirming his return to the job once the holiday is complete.} Once he DOES have the visa in his passport {after his interview in London at the Embassy}, I do not think he is allowed here until he is willing to activate the fiancee visa {and that won't be any sooner then 90 days prior to our wedding on July 28, 2005.} *PLEASE* if I am wrong, someone let me know too!