Citizenship through naturalization: family, marriage.
Moving to United States is a dream of many people however for most the ultimate goal is to become a citizen. This is a lot more complicated than qualifying as a permanent resident so you are going to need to make sure that you are familiar with the procedure. In most cases if you are married to an American it becomes a lot easier.
The first step to becoming a naturalized American citizen is normally to become a permanent resident of the country. There are few exceptions to this rule (find more about the details on The Lawyers Info blog) but in most cases this will be the requirement. In general you can't become a citizen if you have entered the country illegally. Normally once you have lived in the US for a period of five years as a permanent resident you may apply to become a citizen. Any time that was spent in the country before gaining residency status does not count.
In addition to having to be a resident of the US for a period of five years you normally have to be physically present for at least half of that time. That means that you can't apply for residency status and then go live in another country in addition you have to live in the State in which you apply for citizenship for at least three months continuously immediately prior to applying.
The rules are a little bit different for people who marry an American citizen, in this case the waiting period to apply is reduced to three years. In addition if your spouse is out of the country on a official government business, for example they are in the military and stationed overseas of they work for the foreign service then the requirement to be physically present in the US for half of that time is waived.
After the waiting period to apply for citizenship is up you will need to go through a number of steps in order to qualify for citizenship. The first is that you have to prove that you are of good character. For most people this simply means not committing a crime during the waiting period. There are however a few other thing that will get you disqualified as well. These would include openly advocating anarchy or the overthrow of the US government. Being a communist will also prevent you from being allowed into the country.
After you have demonstrated that you are of good character you will need to pass the citizenship test. This covers a lot of ground but it is mostly on the history and the government of the United States. It is not an easy test and it is widely believed that most people who were born in the US would fail, so you are going to want to study hard. Once you have passed the test the last step is to be sworn in as a US citizen.