Who needs to register?
Anyone who entered on a visa for staying longer than 90 days — such as employment (E-9 and others), study, or marriage migration — must register within 90 days from the date of entry. Short stays such as tourism do not need it.
Missing the deadline can lead to a fine and may count against you later when extending or changing your visa, so it is best not to put it off.
Where and how?
You register at the immigration office in charge of the area where you live. Most offices require a visit reservation, which you can make on HiKorea (hikorea.go.kr), the immigration services website. Some employers handle it for their workers, so ask your company first.
What you usually need
The basics are your passport, an ID photo, the application form (available at the office) and the fee. Depending on your visa, you may also be asked for proof of employment or enrolment and a document showing where you live (such as a lease). Requirements differ by visa, so check on HiKorea or by calling 1345 before your visit.
What changes after registering
Once you receive your residence card, many things become easier, such as signing up for a postpaid phone plan, opening a bank account, and health insurance. When you move, you must report your new address, and you also need to report it if your passport number changes.