Congress Asset Management, an employee-owned investment management firm based in Boston, is buying Century Capital Management, Congress Asset Management announced Thursday.

The acquisition, the terms of which were not released, increases Congress Asset Management’s presence in the Boston area. Century Capital is an investment advisory firm with $670 million in assets under management also based in Boston.

Century Capital serves institutions and individuals through two mutual funds: Century Shares Trust, a large-cap growth fund, and Century Small Cap Select Fund, a small-cap growth fund, and separately managed accounts.

“This deal provides us with greater economies of scale and helps position the firm for future growth in a challenging environment for active managers. We were attracted to the strength and diversity of Century’s investment products,” says Daniel Lagan, CEO and chief investment officer of Congress.

As part of the transition, Lanny Thorndike, Century’s managing partner, will join Congress, as will Jeffrey Kerrigan, portfolio manager for the Century Small Cap Value Strategy, and Anand Vankawala, a member of the equity research team.

Founded in 1985, Congress has $8 billion in assets under advisement.