ALEX Katz is a New Yorker through and through. The son of Russian immigrants, he was born and bred in the city and continues to live and work there today. Now approaching 80, his lean, dapper form and energetic demeanour belie his age, while his accent has a distinctive Queens twang. It is from his paintings, however, that Katz the New Yorker truly emerges.

"People in Europe think of my paintings as very American and, more specifically, very New York, " Katz tells me. "But the idea is just to paint what's around you. I had been listening to jazz in the '50s, but by the late '50s it was no longer influential to me. The poetry scene seemed more interesting - actually the painting scene wasn't as interesting as the poetry scene. There were lots of parties, lots of people, lots of social events, and I was painting what I was seeing."

Alex Katz: New York at the Irish Museum of Modern Art features some 40 paintings and aquatints spanning the artist's 50-year career. They fall into two categories: large-scale group and single portraits depicting New York's sophisticated intellectual elite; and night-time city views.

Katz has never fitted into any particular style or movement, developing a distinctive approach entirely his own. Perhaps because of this, his work has sparked strikingly divergent reactions. On the one hand, as he puts it, "I get more bad reviews than any other painter, people screaming in galleries and stuff like that." On the other hand, there are those who seem keen to extol his virtues to the point of hyperbole.

In the catalogue accompanying the exhibition, for example, Imma director Enrique Juncosa describes him as "one of the most influential American painters of our time", while others have dubbed him an "American Munch" or "a Hopper of the second half of the 20th century".

Such varying opinions are not surprising when you consider that Katz is not afraid of championing the somewhat unfashionable concepts of beauty, glamour and style in painting. He is not afraid to admit, for example, that his work is "connected to fashion".

"Sometimes you're closer to it and other times you're not, " he says. "I think I've been fashionable twice in my lifetime. Painting is fashion - it's something that changes every three years."

Katz was born in Brooklyn in 1927 but grew up in St Albans, Queens. He studied at the Cooper Union in New York and then at the Skowhegan School of Painting and Sculpture in Maine, before embarking on a career as an artist. At the time, the Abstract Expressionists were making waves on the New York scene, but Katz followed a different path:

that of a figurative, colourist painter depicting everyday urban life, albeit a glamorous, intellectual, New York style of "everyday". Indeed, he seemed to have more in common with the New York School of poets, such as his good friend Frank O'Hara, than with his contemporaries in the art world.

"The poets and myself were interested in similar things: I was painting everyday things and Frank O'Hara was writing about everyday things. . . I never felt comfortable with the Abstract Expressionist rhetoric - it was too abstract. I wanted something more concrete, " he says. "When I first showed the paintings in the early '50s, an older painter came up to me, trying to give me some friendly advice, and he said, 'Figuration is obsolete and colour is French.' I was not at all interested in what he said. It's basically following your instinct and my instinct was really strong. Instinct is much more real than what this guy was saying."

Katz cites Matisse, Picasso and Bonnard as influences, as well as Japanese artist Utamaro and Egyptian sculptor Thutmose, rather than the Abstract Expressionists or the Pop artists he mingled with in Manhattan. He does, however, admit to adopting aspects of the "grammar" of Abstract Expressionism in his paintings, in terms of their large scale and colour.

But it was Katz's social circle that really inspired him and helped him gain confidence. "I met all these very intelligent people and they all took me seriously.

When you have all these smart people thinking you're pretty good it gives you some confidence, although a good part of the world doesn't get your work at all. But I thought, these people like my work, so I don't have to worry about anything, " he says. "My problem was getting confidence in myself, but it just kept growing and at a certain point I realised that I drew better than 90% of the old masters." Confidence, evidently, is no longer a problem.

The sense of community is an important aspect of his work: "You don't make paintings by yourself.

You're part of a community and they all contribute towards it, " he remarks. Perhaps unsurprisingly, then, Katz is best known for his portraits and the exhibition features images of his wife and son, as well as writer friends such as O'Hara, Allen Ginsberg, Ted Berrigan and Frank Lima. His interest in people, he says, comes from seeing beauty in the world around him. "I like painting people. . . All people have some beauty in them."

According to Katz, the surface is the most important aspect of a painting. "The biggest thing an artist can invent formally is a surface. That doesn't sound like much but Pollock dripped and the world dripped for five years, and then de Kooning splashed and the world splashed for five years, and then acrylic on canvas became popular? My surface is fluid; it's a fluid, flat surface and it's a new surface."

For those who criticise his paintings as being preoccupied with superficiality and surface appearances, Katz responds: "All paintings are seen differently by other people and some people get it and some people don't. . . It's a question of values and I think the surface of life, or the surface of what appears to be life, is the most important thing in the world for a painter and so [the critics'] values are quite superficial because they want a painting about truth or love or suffering or torment, about all those things, but not the most important thing in painting. The most important thing in painting is appearance."

Katz seems to like maintaining his appearance - curiously, he wears gloves when painting. When asked why, he once answered: "I don't like to get my hands dirty." A painter who doesn't want to get his hands dirty? That's New York for you.

'Alex Katz: New York' is at Imma until 20 May