Century City executive search and staffing company Korn/Ferry International is making a big buy, announcing plans Thursday to buy Philadelphia’s Hay Group for about $452 million in cash and stock. It is Korn/Ferry’s biggest acquisition to date.

Under the deal, expected to close by the end of the year, Korn/Ferry will combine its existing talent consulting group with the Hay Group under the Hay Group name. Current Hay Group Chief Executive Stephen Kaye will stay on with the company.

Bringing together the two companies had been in the works for the past eight years, said Korn/Ferry Chief Executive Gary Burnison.

The Hay Group currently has about 3,000 employees. The acquisition will give Korn/Ferry about 7,000 employees all told, Burnison said, though a spokesman noted there may be some layoffs after the deal closes.

Burnison said the company was interested in Hay Group because, “There are very few companies in the world that do what they do.”

“There’s not a preeminent advisor that anybody turns to, so we have the opportunity to create a whole new category,” he said.

Korn/Ferry’s shares rose 3 percent on the day, closing at $35.26.