Safari Books Online, the e-books company based in Sebastopol, has acquired Threepress Consulting Inc., a Massachusetts-based digital publishing software developer.

The acquisition was completed on Jan. 1. Financial terms were not disclosed.

Threepress co-founders Liza Daly and Keith Fahlgren and the rest of the Threepress staff will join the Safari Books Online engineering team, working from their East Coast and Bay Area locations.

"This acquisition is a critical step in support of all three of Safari Books Online's key strategic initiatives: growing and strengthening our base business; developing new products and new markets; and developing truly new ways of learning online," Safari chief executive Andrew Savikas said in a statement.