Globally, a billion people want to learn English, so teach it and you'll be going places, says Nick Jackson

With more than a billion people currently estimated to be learning English worldwide, our language is, without doubt, our biggest and best export. And it follows that, from South Africa to Siberia, there are plenty of great opportunities for teaching the subject.

Not only is teaching English as a foreign language one of the best ways to see the world, it is also a way of meeting some interesting people. "You get people from just about every walk of life on our courses," says David Carr, director of studies at International House in London, the first school to train teachers of English as a Foreign Language (EFL) 50 years ago. The fastest- growing group of trainees, says Carr, are not the gap-year students you would think but middle-aged professionals going through what Carr calls a "midlife career change".

Like any trip abroad, though, you need a passport. In this case, a Teaching English as a Foreign Language (Tefl) qualification. But before you even start, you need to find your way through the forest of acronyms that constitute the various courses. Should you go for Celta, Delta, Felt, TKT, Tesol...?

First ensure that what you are applying for is in fact a course. The Teacher Knowledge Test (TKT) is often slightly misleadingly listed alongside training courses. It might look like a tempting option, being much cheaper and quicker than the others, but is generally considered to be inappropriate unless you are an experienced teacher. It is more of a refresher test than a course.

Most teaching jobs require you to have passed one of two intensive, month-long courses: the University of Cambridge's Certificate in English Language Teaching for Adults (Celta); and Trinity College London's Teaching English to Speakers of Another Language (Tesol). These are equivalent qualifications. They give you a full grounding in English language, particularly in how to explain the grammatical rules that you may take for granted, and, more importantly, teach you how to teach, which makes up the majority of both the courses.

Celta and Tesol are essential if you are planning to freelance or find work once you are in the country. But that is not the only way to find teaching work. If you want to get away quickly, some organisations offer a package: arranging work for you abroad, giving you basic training before you go, plus extra training on the job once you get there.

Saxoncourt is a global training company with schools in London, South Africa and New Zealand. As well as offering standard Celta training, it finds work for untrained Tefl teachers to go to Japan, China and Taiwan, and offers them a free intensive one-week course, the Foundation in English Language Teaching (Felt). Once out in the East, teachers can expect to be given help on the job.

Phillipa Giddings did a Felt course with Saxoncourt before going to teach in Taiwan three years ago. "I found it very helpful," she says. Since then, she has spent little time in the UK. After 18 months teaching in Taiwan, she moved to Spain, and then Russia to teach. She has only been back in the UK for a fortnight and is already planning her next teaching trip, this time to Libya. "It's a great lifestyle," she says. "You get to teach, which I really love, and travel, which I also really love."

For school-leavers or graduates, teaching English as a foreign language is also a great job to be able to fall back on when you return to Blighty. Anyone who lives in London will be aware of the thousands of foreigners who come to the capital to learn English. Celta and Tesol graduates can earn around £14 an hour, double a temping typist's salary, for example, for working at one of the dozens of English schools that pack London's West End.

Ed Barnett, 27, teaches English at International House in London. He says that Tefl training is not just for a gap year or a summer in the sun, but "an incredibly versatile skill to have". Over the two-and-a-half years he spent working for VSO as an English teacher in Cameroon, Barnett also found himself working on various development projects, building a school library and study room from scratch, setting up a teaching resources centre, and arranging for second-hand textbooks from International House to be sent on to Cameroon.

He is now looking at a career in education policy in international development, although it is obvious that he misses his school in Cameroon. "There's a vibrancy and energy there," he says. "And working with those people was a very rewarding experience."