If you are US citizen and would like to get married with an alien (non-US citizen), you can either get married in US or outside the US.

• Follow the K1 visa application process
  
  
• Get married within 90 days of alien fiance arriving in the US
  
  
• After marriage, file Form I-485, Adjustment of Status.
  
  

If you got married outside the US, follow the procedure given below to bring your spouse to USA and to get him/her green card:

• File Form I-130, Petition for Alien Relative.
  
  Once USCIS receives complete application, it will send you a receipt called I-797C, Notice of Action. Once you receive that, you can follow either of the paths below:
  • Immigrant Visa
    • Wait for I-130 to get approved.
      
      
    • Consular Processing
      Alien spouse goes through consular processing and enters the US with immigrant visa.
      
      
  • K3/K4 Visa
    • Follow the K3 visa application process
      
      
    • Once the spouse is in US, file Form I-485, Adjustment of Status.
      
      

While immigrant visa process is overall faster to get the green card (typically, 1 year to 18 months, but it all depends upon the USCIS, consulate etc.), they (spouse/children) enter the US with green card.

Through K3/K4 visa, spouse and children will be able to arrive in the US in around 6 to 8 months (again, it depends), it will take several years to eventually get green card through adjustment of status.

If you have children between the ages of 18 and 21 who are not the natural children of your US spouse-to-be, choose a fiance visa (K1 or K3). Due to strange twist in immigration laws, children under 21 can accompany a fiance on their visa, but only children under 18 can accompany a just-married spouse on an immigrant visa - if the US citizen spouse is not the children's biological parent.

While comparing the choices, where available, Direct Consular Filing (DCF) is preferred as it is quickest. It is similar to immigrant visa but several steps are combined into one. However, DCF should be used for straightforward cases only. If there are any adverse factors, such as criminal record, serious illness, or previous out of status time, DCF may not work. Also, the procedures at various consulates keep changing and they may or may not be allowing DCF at any given time. DCF is available only to US citizen-foreign national marriage and not available for permanent residents.

If you have been married for less than 2 years when you arrived in the US on an immigrant visa or are approved for Adjustment of Status after arriving in the US, you will be given a conditional green card that expires after 2 years.

90 days before the expiration of 2 years, you will have to apply to remove conditions on the green card and apply for permanent one. USCIS may interview both of you separately to determine whether the marriage is real. If they find out that it was fraud, you will lose your green card and will have to leave the US.

If your marriage is 2 years old when you arrive in the US on an immigrant visa or are approved for Adjustment of Status after arriving in the US, you will get a permanent green card. (That card eventually expires in 10 years and have to renew it. However, just the card expires and your permanent resident status does not expire.)