There are multiple types of visas for foreign nationals looking to enter South Korea. The most common is the K-ETA or Korean Electronic Travel Authorization.
The K-ETA allows citizens of 122 countries, including the US, to visit South Korea for stays of up to 90 days for tourism and designated business purposes. Valid for two years, it’s a multiple-entry authorization that allows you to enter and leave the country multiple times on the same visa.
The K-ETA is not extendable or renewable, but as it is multiple-entry, you can leave and then reenter the country at the end of 90 days. If your K-ETA expires, you can apply for a new one outside the country. Processing and approval generally take 48 to 72 hours.
If you plan to stay longer than 90 days to work or study, you’ll need to apply for an Alien Registration Card. Don’t lose it—you’ll need to return the card to immigration officials when you leave.