Both immigrant and non-immigrant visas allow a foreign national to enter the US. However, the two types of visas vary widely. Non-immigrant visas allow someone to request Department of Homeland Security officials at US ports of entry permission to enter the US temporarily. Non-immigrant visas are usually designed to allow someone to stay in the US for a temporary time. These visas usually do not permit someone to set up residency in the US and many non-immigrant visas also do not permit visitors to work in the US, although some do allow work authorization. There are more than 20 non-immigrant visa categories, and most reflect the many reasons why someone may wish to enter the US for a short period of time. If you want to travel to the US to study, take part in business, travel, or to take part in temporary work, you will generally need a non-immigrant visa. The only exception to this is if your home country is part of the visa waiver agreement with the US. It is important to keep in mind that non-immigrant visas only allow a person to seek entry into the US. They do not guarantee entry and visa holders may still be denied entry to the US by Department of Homeland Security and other border officials
The immigrant visa category in the US is intended for those nationals who wish to live and work in the US permanently. Also known as the green card, the immigrant visa is intended for those who wish to relocate to the US. It is generally more difficult to get an immigrant visa than a non-immigrant visa. While most B-1 non-immigrant visa applicants are accepted by the US, the US only accepts some immigrant visa applicants each year and places caps or limits on the number of immigrant visas granted. While there are more than 20 non-immigrant visa categories, there are only four categories for immigrant visas. You can get an immigrant visa through employer sponsorship, family sponsorship, immediate family sponsorship, and through a special immigrant category. There are special requirements for each category.