Rootlessness is what interests David Greig, whose play, Outlying Islands, opens in Limerick this week. And living and working in his native Scotland means he doesn't have to write about being Scottish, he tells Sara Keating

Scottish playwright David Greig is as difficult to define as are his characters, and they are a motley crew of men and women searching for a sense of belonging in the world. They are amnesiacs, diplomats, astronauts and men at sea; people with no roots and no homes; people who have no idea who they are. While Greig himself projects a steely sense of self-conviction far removed from the quests of self-discovery embarked upon by his characters, he is as complex as his various protagonists, although the journey towards self-awareness that preoccupies his characters seems long behind him.

A prolific public playwright with a body of work that includes 20 published plays, Greig is willing to discuss anything, from his unusual background to his own spiritual philosophies to the merits of his peers in contemporary Scottish theatre. He is also open about identifying with the humanist themes of self- discovery in his work. In dulcet tones that sound like those of a one-time British public schoolboy he traces his plays' concern with identity, belonging and the search for home to a peripatetic childhood divided between Edinburgh, Africa, and an isolated part of north-eastern Scotland.

"Almost every single play that I've done is about someone or somebody trying to work out who they are or where they belong," he says. "And when I look back it seems very obvious that that comes from the nomadism in my childhood. I mean, when you hear my voice, you'll be able to tell that it doesn't sound very Scottish, but I've lived all my adult life in Scotland, all my relatives are Scottish, and I think of myself as Scottish - yet wherever I go I'm identified as being not Scottish.

"So there's a kind of thing where, for reasons of geographical and familial accident, I appear not to belong where I belong, and that has always struck me as an interesting, sometimes uncomfortable and sometimes illuminating position."

One sense in which this position has been enlightening is in the objectivity it has given him about ideas of cultural identity and the common (mis)understanding that place - the home we live in, the city we come from, the country we identify with - is an anchor of our self-definition.

"Having a sense of home or what home might mean is one of the big questions of our time," he says. "There's a sense of a loss of home, in the places that people leave behind, but also home in the sense of the places where we live, which are constantly changing around us, so we can't be sure where we are any more or where we fit in. But I think it's more important to be sceptical of that feeling, and I'm quite anxious not to be identified as a nationalist, because I'm really not.

"I mean, Pyrenees [which has just completed a successful run at the Project Arts Centre] is quite cynical about place or the idea of being Scottish or Welsh or west country. The Man is horrified when he finds out he's Scottish, what with the stereotypes of jocks. And in Outlying Islands [which begins a two-week run at Limerick's Belltable Arts Centre this week] Robert's utopian idea of flying away, unrooted from land, is an extreme of not being connected in such a way to any place."

GREIG IS VOCAL about how contemporary Scottish theatre is reflecting the idea that identity is fluid and cannot be pinned down to a particular place as an anchor for individual self-definition. He points in particular to the function of the National Theatre of Scotland, founded in 2004 amid much controversy when it decided to exist as a touring entity rather than as a receiving house.

"I think the worst thing that they could have possibly done would have been to build a national theatre and to put plays on in it. It would have been so-oooo 19th century; it would have been hopelessly out of date," he says. "The thing that's great about the National Theatre of Scotland is that it recognises the complexities of identity in the 21st century, and as the theatre is literally not set in stone as a building, so the Scottish identity that it reflects is not set in stone.

"The National Theatre of Scotland is equally at home in a skateboard park in Aberdeen as it is amongst asylum seekers in Glasgow, as it is where I am now, doing a childrens' show in Easter House in an area of Glasgow that is not wealthy, performing for kids that do not get to go the theatre very often.

"For me, the thing about the National Theatre of Scotland is that it is without walls, that it is adaptable and that it recognises identity as fluid, and so the theatre itself is fluid to represent that."

Of course, being Scottish - even in some fluid, indefinable sense - is still a fundamental part of Greig's identity and a shaping factor in his work.

"I had a choice when I was about 22, when I first started having plays professionally produced," he says. "I decided that I had to stay in Scotland. I could have gone to London - that probably would have been a wiser, more lucrative choice - but whatever it was, at some gut level I knew that I couldn't do that. I felt this very strong belief that the people that I was writing for were the audience in my home . . . city . . . country . . . I don't know. I felt that by writing for them that I was liberated not to write about them.

"I think perhaps if I'd been in London I might have written more directly about Scotland, in a more cliched way or a more nostalgic way. I felt that living in Scotland, writing for an audience that I was living amongst, I was free to write about whatever came into my head. I needed to be at home in order to write freely."

And home, as the characters in Pyrenees, Outlying Islands and Greig's many other plays reveal, is not necessarily where you're from, but where you find yourself to be.

Outlying Islands, by David Greig, runs at the Belltable Arts Centre, Limerick from this Wed until Sat, Sept 23. Critical Voices 3 presents a post-show conversation between David Greig and Philip Howard, of Edinburgh's Traverse Theatre, at the Belltable on Fri, Sept 15 at 9.30pm