Deep Green Resistance was founded by the authors of a book of the same name, a nasty set of activists named Derrick Jensen, Lierre Keith, and Aric McBay.
They advocate a method known as “decisive ecological warfare” designed to destabilize and ultimately overthrow capitalism, industry, agriculture and civilization itself. Their unambiguous aim is to return the earth to a more “sustainable” position. In caves, presumably.
DGR calls itself an “above ground” eco-activist movement and tries to associate with many fringe enviro or aboriginal activist organizations. However, the book and its authors also call for parallel “underground” operations, which include isolated and covert operative cells. Their above ground arm seeks to support activist movements publicly, but their underground arm may recruit from these same groups.
Unlike previous ecological terrorist movements, they advocate for destruction of property and, if need be, assassination of the purveyors of industry. They justify it in that industry proponents are killing people already and as such are potentially viable targets. If innocents are killed, their excuse is that industry caused the deaths, not them. Their valued targets are those critical ties to infrastructure which could cause cascading effects to industry if impacted. These include power substations, pipelines, lines of communication, transportation hubs or water control.
Brian Lilley interviewed McBay on Byline in 2011 and wrote a blog post on the book.

They are currently known to be operating in opposition to the Northern Gateway, but were also present during the Rexton, NB anti-fracking debacle.