Using symplectic geometry and Nakajima's quiver varieties, Maulik and Okounkov have associated an R-matrix to any quiver. For quivers of Dynkin types, we recover the rational R-matrices and the corresponding Yangians. For general quivers, there is no algebraic description of the corresponding quantum groups. We'll explain a conjecture relating these new quantum groups to a new family of algebras called cohomological Hall algebras. We'll also describe some recent progress toward the proof of this conjecture.