If you are an American looking to become an expat and move to Belgium, then there are a few things you must do to prepare before you leave the United States for Belgium.
If you plan on making the country of Belgium your permanent residence, then you need to go through a formal process so that you can stay and live in the country legally, otherwise you can be thrown out and denied entry for all time in the future. The first thing you will need to work towards acquiring in your journey to move from the USA to Belgium is that you must first secure yourself a visa to make sure that your stay is in fact legal. Any American, which does not also possess citizenship of a member country of the European Union, that intends to stay within the borders of Belgium for a period greater than 90 days will need to have a visa before entering the country. To get this visa, you will have to apply for it at the consulate or embassy in the United States. You cannot obtain the visa if you are already within the borders of Belgium. The visa must be applied for and obtained in person, only by the applicant and not someone else on their behalf, within your home country, which of course would be the US.
There are two different types of visas that can be applied for. They are the short stay visa and the resident visa. Do not mistakenly apply for the short stay visa. The short stay visa is only valid for a period of up to 90 days, and Americans do not need a visa if they are only staying in Belgium for a period no longer than 90 days. The visa that you will want to make an application for if you want to move to Belgium from the United States is the resident visa. This is the only visa that allows you to legally stay in the country past the initial 90 day period.
The process of getting your resident visa reviewed usually takes at least 3 months, but can take a period of time much longer. It is important to keep this in mind before you apply. To make sure the process runs as smoothly as possible, there is a fairly standard list of requirements in regards to documentation that is regularly requested. Typically, the following items are required to be submitted with your application for the long term stay resident visa.
You definitely must be in possession of a valid passport, which does not expire for at least 3 months after you will have been in the country one year of your arrival date. Other things you will likely need with your application are: you birth certificate as well as a translated copy of it, a certificate of good health, some passport-size photos, either a work permit or proof of application of a work permit if you are planning on working, proof of professional ability to practice your trade if you will be self-employed, a certificate of good conduct showing that you have no criminal record, proof of financial means if you are not going to be working, valid health insurance, proof of admission to a university if you plan on being a student and proof of an agreement with a host family if you plan on being an au pair as they will be providing you both employment and a place of residence most likely.
You can also be approved for a resident visa if you are coming to Belgium to marry or live with a Belgian citizen, or simply someone that is already legally residing in Belgium. You will just have to show documentation that proves that you will be living with this person and that they can financially support you.