Teaching English in Japan is one of the only ways to get a long term visa to stay in Japan as a foreigner and it is one of the most popular ways to visit Japan for something other than a short vacation.
Because Japan is such a popular place for people go to when they want to travel the world and experience a new culture and way of life, many people want to travel there. However, Japan does not accept individual for long term stays very often due to overpopulation. One of the exceptions to this is to teach English in Japan. There is a high need for English teachers, since it is such an important language for both the world and Japanese economy. So Japan has opened its doors to those accepted to programs that allow you to teach English.
However, just because there is a high demand for teachers does not mean they accept everyone. Japan has very high standards for its teachers. The resume of someone hoping to teach English must be very good, with recommendations, a firm grasp of Japanese, and many extracurricular activities. They also are very specific about the health of the applicant. If you are currently taking or have ever taken any type of psychiatric medicine, they are unlikely to accept you regardless of your resume. You will also want to apply early as teaching spots fill up very quickly, so even if you apply before the deadline the spots may already be filled and you would be on the waiting list.
The average salary is approximately 250,000 yen. Some teachers receive apartments from their schools, though not all of them, and others will pay the costs of a work visa. Japan also has national health care, so you do not need to worry, but you must have a job otherwise you are not covered. You get 4 weeks of vacation, and these are usually preset weeks. The work week is approximately 20 to 25 classes of 50 minutes.