The opportunity to work or live in the United States is an incredible moment for many people. When that chance is afforded to them, though, they likely have to leave their family and loved ones behind to seize the opportunity. Thankfully, there are ways for immigrants to extend similar immigration opportunities to their family and loved ones, which can help the family reunite and move forward as a happier unit.
There are two ways to acheive this goal: consular processing and adjustment of status. The first step to be taken is for the spouse to be formally recognized with a legal and official marriage. This is the first critical step. It may seem simple and obvious, but that doesn't make it any less important. Couples who intend to marry soon won't be given a pass.
With that step confirmed, you have to file a form, called I-130, on behalf of your spouse. There is also a fee, totaling $420, to complete this stage. Next, you will have to get an immigrant visa number for your spouse. The time it takes to get this number varies wildly, and depends greatly on your status. If you are a U.S. citizen, your spouse will receive special consideration (i.e. an expedited process). However, if you are a permanent resident, then your spouse will be placed on a waiting list.
Once your spouse receives this number via the status petition, the next step depends on where he or she is located. If your spouse is outside of the U.S., he or she will have to go to the local U.S. consulate to complete the visa petition (called "consular processing"). If your spouse is in the U.S. legally, then you can apply for adjustment of status via Form I-485 (this can be done at the same time as filing I-130).
Source: FindLaw, "Spouse Immigration," Accessed July 7, 2015