Due to a combination of long processing times for green cards, and the legal notion of "immigrant intent", H1-B is commonly used as a bridge to a green card. A

Due to a combination of long processing times for green cards, and the legal notion of "immigrant intent", H1-B is commonly used as a bridge to a green card. Any US visa which isn't a green card (e.g. tourist visas, student visas) is considered a non-immigrant visa. You can only apply for, and enter on a non-immigrant visa if you don't have immigrant intent. If an international student, for example, applies for a green card, this shows immigrant intent and they could find it difficult to renew their student visa or even to re-enter the US after traveling. Obviously this wouldn't be a problem if the green card itself were quickly approved, but the process is bureaucratic and can take years even for people with advanced degrees. H1-B visas, on the other hand are one of the few visa classes that allow "dual intent", meaning that while they're non-immigrant visas, H1-B holders are also allowed immigrant intent. Which makes it a good visa to have before starting the green card process, if you want to be able to travel (e.g. to visit family) while your application is pending.