Nonimmigrants are subject to multiple sets of rules governing their stay and activities in the U.S. Each set, or nonimmigrant category, is denoted by a letter and sometimes a number as well if there are sub-categories. However, a petitioner must first file a petition with USCIS to qualify any alien (not including dependents) for most work-related classifications, including the O or P categories.

Filing a petition takes planning. The petitioner - who cannot be the alien - must select the appropriate nonimmigrant classification and gather the required forms and evidence, including a union consultation if needed. The petitioner must know which of the two USCIS regional service centers to use, provide the correct filing fee, complete the forms properly, submit the correct number of copies, and file sufficiently far in advance of the required entry date to account for processing times, visa application times, and the unexpected.

Following the rules carefully should yield an I-797 Approval Notice to forward to the alien. If abroad, the alien can then complete a visa application form, pay any necessary fees, and apply for a visa in the category selected. With the visa, the alien will be able to appear for inspection at a U.S. preflight inspection facility (PFI) port of entry (POE) or border post. Again, hopefully, the alien will be admitted in the appropriate status, for the required length of time. Following essentially the same process, aliens already present in the U.S. on a visa (but not the Visa Waiver Program) may, for the most part, change to the appropriate status and, if need be, extend their stay.