In order to teach legally in Korea, you will need have an employer sponsor a work visa. It is possible to come to Korea without a job on a tourist visa, however once you find a sponsoring school, you will have to leave the country in order to get a valid work visa.
Korea has some complicated tourist visa rules, so check with a Korean embassy to find out how long you will be permitted to stay. As a general rule most countries’ citizens are permitted to stay up to 30 days without any special visa requirements. Australians and EU nationals can stay up to 90 days and Canadians for up to six months. This information is meant to be a general guideline, be sure to verify the validity of your own particular tourist visa before you go.
Upon arriving in Korea with a work visa, you will need to visit Korean Immigration to get a residence certificate and a re-entry permit within 90 days of entry.
Be wary that some Korean employers will ask for your passport telling you that they need it to process your work visa or other documents. This is not required. Some schools have been known to withhold visas to ensure that your contract obligations have been met. Of course, it is possible to break your contract and leave Korea at any time you see fit, but your work visa is not transferable to another employer. If your work conditions are unbearable you will need to secure another employer and get another visa in order to remain in Korea.
Make sure you do your research with your future employer and compare many different teaching positions. It is not fun being stuck in a terrible school for a year, particularly if they are not fulfilling their salary and benefits promises. Schools hold all the power with regards to visas in Korea.
TEFL English teaching job listings in Korea
A general overview of what to expect teaching English in Korea
Detailed living costs for teaching English in Korea.
Interviews with English Teachers in South Korea
Korea (Visa and Requirements)
Official Korean Website
Korean News (Chosun)
Korean News (Korea Herald)
Korean News (Korea Times)
Korvia.com Government approved site for public school jobs.