Calvin Coolidge famously said that the business of America is business. For Robert Walsh, the business of New York is small business.

“There are more than 200,000 small businesses in our city,” the commissioner of New York City’s Department of Small Business Services said. “That represents 98% of all businesses in New York.”

Those businesses employ 1.5 million people in all five boroughs, or 50% of the workforce. That translates into $4.5 billion in tax revenues annually in a city whose gross domestic product is more than $500 billion. If New York were a nation, the wealth of its 8.1 million people would make it the 16th richest of the world’s 191 countries. Of course, with only 309 square miles, the city would physically be very nearly the smallest.

Such facts and figures seem to come naturally to Mr. Walsh.

“It’s always been this way,” he said. “Ever since I was a kid growing up in Bensonhurst, the city’s history fascinated me. Fortunately, I also got the opportunity to make a contribution to New York’s civic life. I believe in public service.”

Mr. Walsh has a certain earnestness. For a reporter brought up in India on a diet of Hollywood movies, the commissioner’s demeanor comes through as quintessentially can-do American.

One of seven children of an Irish commercial artist, Arthur, and an Italian mother, Theresa, Mr. Walsh grew up as Irish as one possibly could in an Italian neighborhood in Brooklyn. There was the community church. There was the influence of Jesuit priests who, he said, “inculcated in me a sense of service to the community.” There was Fordham University, where he obtained a graduate degree in – what else? – public administration.

That led to eight years in Mayor Koch’s administration as executive director of the Urban Fellows Program, chief of staff at the Department of Transportation, and assistant director for citywide administrative services in the mayor’s Office of Operations.

He then became executive director of the 14th Street/Union Square Business Improvement District and Local Development Corporation. Union Square had suffered from neglect and blight during the 1980s, and Mr. Walsh helped put it on the map as one of the most dynamic neighborhoods of the city.

“I’m proud of Union Square’s transformation,” Mr. Walsh said, omitting any reference to the accolades he received for launching one of America’s most effective examples of civic renewal.

“My team and I were determined to take back the neighborhood,” he said. “It wasn’t just about bricks and mortar but, more importantly, it was about people’s lives. It was about making their lives better, safer. It was about celebrating diversity.”

As part of his assignment, Mr. Walsh helped create the Washington Irving High School Business Advisory Council, which continues to provide mentoring services and summer jobs programs for thousands of students from socioeconomically deprived communities.

Mr. Walsh was subsequently recruited by the Bank of America Corporation to work in North Carolina as president of Charlotte Center City Partners. The job involved the promotion and enhancement of business, cultural, retail, and residential initiatives in Charlotte’s central business district.

His performance came to the attention of Daniel Doctoroff, who had joined the administration of Mayor Bloomberg, who was then newly elected. Mr. Doctoroff invited Mr. Walsh to see the new mayor.

“I’d never met Mike Bloomberg – I didn’t even know if he knew that I was a lifelong Democrat,” Mr. Walsh said. “The job interview lasted for an hour.”

As Mr. Walsh walked down the steps of City Hall, he felt someone’s hand on his shoulder.

It was Mr. Doctoroff.

“He wants you back up there,” he said to Mr. Walsh.

Upstairs, outside the mayor’s office, Police Commissioner Raymond Kelly – whom Mr. Walsh knew from his earlier tenure in city government – was waiting to see Mr.Bloomberg.When the mayor saw him, Mr. Kelly said: “You talking to this guy?”

Then he started saying pleasant things about Mr. Walsh.

The mayor simply extended his hand to Mr. Walsh and said, “Say yes.”

“Yes,” Mr. Walsh said.

“Good, now you’re my commissioner of small business services,” Mr. Bloomberg said.

As Mr. Walsh turned to leave the room, the mayor said: “Hey, Walsh.”

Mr. Walsh faced him again.

“Don’t screw it up,” Mr. Bloomberg said.

Recalling the episode over lunch, Mr. Walsh smiled hugely.

“For the last four years, I’ve been trying not to screw it up,” he said.

Few people in New York would accuse him or his 250-person department, which has an annual budget of $100 million, of screwing things up.

Among other things, Mr. Walsh expanded the city’s jobs training program. He has re-energized the city’s 51 “business improvement districts,” the so-called bids. His department develops public-private partnerships, and the bids offer delivery of supplemental sanitation services, graffiti removal, security, and capital improvements that have helped revitalize commercial corridors.

“Small businesses are truly the backbone of New York’s commerce,” Mr. Walsh said. “I only have to look around my neighborhood and see how much economic and cultural vitality these businesses generate.”