When renting an apartment in Korea — especially in Seoul's expat neighborhoods like Hannam, Itaewon, and UN Village — you'll encounter a uniquely Korean concept: the housing deposit system (보증금, boJeungGeum). Unlike most countries where deposits are one or two months of rent, Korean deposits can range from 10 million to over 1 billion KRW, directly affecting how much monthly rent you pay. This guide explains how the system works, why landlords prefer it, and how foreign tenants can use it to their advantage.