Gelesis is a privately held biotechnology company located in Boston, Massachusetts. The company is developing orally administered medical devices made out of food ingredients that, when taken with water, expand in the stomach to give a feeling of satiety. The particles mix with food, keeping it in the stomach longer and slowing the absorption of nutrients in the small intestine. Gelesis' first investigational device, Gelesis100, is currently in proof of concept clinical studies for the treatment of obesity.

Gelesis was founded by PureTech Ventures. The company’s technology is based around technology out of the University of Salento in Italy. Alessandro Sannino, a professor of engineering at the University of Salento, is a co-inventor of the technology. Gelesis has raised $42 million to date through four rounds of funding, with the most recent round of $12M announced in May 2014 with PureTech Ventures, Pritzker/Vlock Family Office, and other undisclosed investors participating.