The notion of a GKM graph was introduced by Guillemin-Zara [1], motivated by a result of Goresky-Kottwitz-MacPherson [2]. A GKM
 graph is a regular graph with directions assigned to edges satisfying certain compatibility condition. The 1-skeleton of a simple poly
 -tope provides an example of a GKM graph. One can associate a GKM graph $\mathcal{G}_M$ to a closed manifold $M$ with an action of a 
 compact torus satisfying certain conditions (those manifolds are often called GKM manifolds). Many important manifolds such as toric 
 manifolds and flag manifolds are GKM manifolds. The GKM graph $\mathcal{G}_M$ contains a lot of geometrical information on $M$, e.g. 
 the (equivariant) cohomology of $M$ can be recovered by $\mathcal{G}_M$. I will present an overview of some facts on GKM graphs.