Also, what is the difference between a foreigner marrying a green card holder vs a citizen of the US?
If a foreigner marries a green card holder in the US, will the foreigner also be entitled to a green card at some point?
Yes. In theory. Congress can, however, change the system by legislation before someone gets a visa that they have applied for at any time, which could prevent some applicants from ever receiving a visa.
what is the difference between a foreigner marrying a green card holder vs a citizen of the US?
Someone marrying a citizen of the U.S. has a higher priority that is not subject to categorical or country based quotas. This means that delays in these visas being issued are shorter:
If your spouse is a U.S. citizen and you currently live in the United States, it takes on average 11-20 months to get a marriage-based green card. Spouses of U.S. citizens living in the United States can file their I-130 and their I-485 at the same time.
If your spouse is a U.S. citizen and you currently live outside the United States, it takes on average 7.5-13.5 months to get a marriage-based green card.
A foreigner marrying a green card holder is subject to both categorical and country based quotas which can greatly delay the processing of their application, but, in theory, will eventually cause a lawful permanent resident visa to be issued to the foreigner seeking to marry the lawful permanent resident. The delay is especially long if the foreigner is from Mexico or the Philippines.
According to this source:
The total processing time for obtaining a marriage based green card when one spouse is a permanent resident and the other is a foreign national seeking a green card, both living in the U.S., ranges from 29-38 months.
Another source (the same one used for the delays for U.S. citizen spouses), however, states:
Spouses of green card holders will have to wait for a green card to become available after their sponsor files form I-130 and before they can apply for a green card from either within the United States or at a U.S. consulate abroad. In most cases, it takes about two years for a green card to become available, and the entire process takes around three years. It can take slightly longer for citizens of Mexico, China, India, and the Philippines.
If your spouse is a green card holder and you currently live in the United States, then you will wait about 11-20 months to receive your green card.
If your spouse is a green card holder and you currently live outside the United States, then you will wait about 13.5-35.5 months to receive your green card.
This answer provides an overview of the overall U.S. immigration system for green cards and otherwise, because it is easier to understand immigration in the specific category asked about in the context of the overall picture.
Overall, the U.S. grants about one million people a year lawful permanent resident visas (a.k.a. "green cards") under several distinct priority systems, some of which have quotas and some of which do not. It also grants a great many temporary visas.
(Source for the images above)
Family Based Immigration
The biggest single category of these lawful permanent resident visas are granted based upon a family relationship with a current U.S. citizen or lawful permanent resident.
The number of lawful permanent resident applications that can be granted each year on the basis of family relationship other than being immediate relatives of U.S. citizens is limited a quota of about 480,000 visas a year created by U.S. immigration law and there is a priority system for those applications. In fiscal year 2021:
A total of 757,206 petitions to establish a family relationship with a U.S. citizen or green card holder (Form I-130) were received in FY2021, with a steep uptick in quarters three and four (USCIS received 149,173; 148,039; 243,753; and 216,241 petitions in quarters 1 through 4, respectively). Overall, denials of I-130 petitions fell in FY2021 to just under 11 percent.
USCIS received 300,162 adjustment of status applications on Form I-485 in FY2020, but only 288,668 in FY2021. The agency approved 266,080 applications, a significant increase from the approval of 229,676 seen the year before. In further good news, 44,181 applications were denied in FY2021, down from 53,032 denials last year.
However, this progress was not enough to make a meaningful dent in the family-based I-485 backlog, which stands at 349,350 pending cases at the close of FY2021 — a 52% increase over FY2020. Current estimates place the family-based green card backlog – including the USCIS and Department of State green card backlogs — at 1.6 million.
A spouse of a lawful permanent resident of the United States (a.k.a. a "green card holder") is eligible to apply to be a lawful permanent resident of the United States on that basis, and so in a spouse of a U.S. citizen. (Source)
If you are the spouse, minor child or parent of a U.S. citizen, this application can be granted to these people who count as "immediate relatives of U.S. Citizens" without considering the quotas established by U.S. immigration law for other kinds of lawful permanent resident applications based upon family relationships.
In family based visa application system for people other than immediate family of U.S. citizens there are five different layers of priority, a spouse of a lawful permanent resident has second priority after the unmarried adult children of U.S. citizens:
First preference (F1) - unmarried sons and daughters (21 years of age and older) of U.S. citizens;
Second preference (F2A) - spouses and children (unmarried and under 21 years of age) of lawful permanent residents;
Second preference (F2B) - unmarried sons and daughters (21 years of age and older) of lawful permanent residents;
Third preference (F3) - married sons and daughters of U.S. citizens; and
Fourth preference (F4) - brothers and sisters of U.S. citizens (if the U.S. citizen is 21 years of age and older)
Country Quotas And Backlogs
In addition to those priority categories there are also priorities and quotas within the overall allowed family immigration visa quota based upon the applicants' countries of origin.
For the capped preference categories in the family and employment streams, U.S. law imposes a limit on how many immigrants from any particular country can receive green cards in a given year. Under the per-country cap set in the Immigration Act of 1990, no country can receive more than 7 percent of the total number of employment-based and family-sponsored preference visas in a given year. There are no per-country limits for uncapped categories, such as immediate relatives of U.S. citizens.
Because of the numerical caps and per-country caps on certain green-card categories, there are significant waits for some categories, with sharper effects on a few countries. For example, as of April 2019, the wait for U.S. citizens to sponsor adult, unmarried children was more than seven years for most parts of the world, but was 12 years for relatives from the Philippines—and more than 21 years for those from Mexico. As of November 2018, there were 3.7 million people waiting in line abroad for a family-sponsored green card, and 121,000 awaiting an employment-sponsored green card.
Thus, a lawful permanent resident's spouse applying to become a lawful permanent resident needs to be able to fit in both a quota for their visa priority level and also a quota for their country of origin. These combined quotas often give rise to large backlogs, especially for immigrants from Mexico and the Philippines.
Non-Family Based Green Cards
There are also more than half a dozen other major categories of grounds upon which someone can apply for lawful permanent residence status in addition to a family relationship with a U.S. citizen or lawful permanent residence of the U.S.
Some of the main other categories of lawful permanent residence visa applications are those based upon ordinary employment (about 140,000 a year), employment as a religious worker or journalist, those based upon refugee, asylum, crime or abuse victim status, connections to services done for the U.S. military in Afghanistan or Iraq or in NATO, diversity visa lottery winners (about 55,000 a year), and a host of other niche grounds for applying for this status that have accumulated on an ad hoc basis over time.
The priorities and quotas for lawful permanent resident visas granted on these other grounds are more or less independent of the priorities and quotas that apply to applications for lawful permanent residence status based upon a family connection to someone who is already a U.S. citizen or lawful permanent resident.
There were 45,897 applications for employment-based green cards submitted to USCIS in the final quarter of FY2021, a dramatic increase from the 26,433 applications received during the same period last year. In total, USCIS approved 161,438 employment green cards, a 1,077% increase from 13,709 the previous year.
Employment-based green card backlogs in particular have become an unfortunate fixture of the U.S. immigration system, largely due to regulations that cap the number of immigrant visas (green cards) issued to citizens of any one nation, as well as the overall green card caps put in place by Congress that were discussed earlier. By law, USCIS can issue up to 140,000 employment-based green cards each year, plus any unused family green cards from the previous year.
As a result of the steep decline in family-based green cards issued during FY2020 discussed above, 122,000 family-preference visas went unused and were added to the 2021 cap on employment-based visas, which raised the total available to 262,000.
Due to administrative processing backlogs and other paperwork snafus, however, about 200,000 available visas under the quotes have not been used in recent years.
The predominant source for the visa related statistics above which are not otherwise attributed is here.
In addition to lawful permanent resident visa, the U.S. also issued a wide variety of other temporary visas, some of which, like vistor's visas from countries with whom the U.S. has a favorable immigration relationship and student visa, are granted almost as a matter of course, and others of which, like H1-B technology worker visas, are extremely scarce and hard to obtain.
Change In Status Considerations
Special rules apply to transitioning from one kind of visa to another and to the treatment of undocumented immigrants who seek to obtain lawful immigrant status with an appropriate visa (particularly a subset of the applicants in the Deferred Action for Childhood Arrivals (DACA) program).