Zoom-Meeting: https://wwu.zoom.us/j/97461739978 Abstract: G_2-structures on 7-manifolds are defined by a closed positive 3-forms and constitute the starting point in various known and potential methods to obtain holonomy G_2-metrics. Although linear, the closed condition for a G_2-structure is very restrictive, and no general results on the existence of closed G_2-structures on compact 7-manifolds are known. In the seminar I will review known examples of compact 7-manifolds admitting a closed G_2-structure. Moreover, I will discuss some results on the behaviour of the Laplacian G_2-flow starting from a closed G_2-structure whose induced metric satisfies suitable extra conditions.