In dimension seven, manifolds with special holonomy G2 play an important role in both mathematics and physics. Aside from certain construction of G2-metrics, properties of the moduli space of G2-metrics are barelyknown. In the first half of the lecture series, I will discuss basics in G2-manifolds from scratch, including geometric and topological properties. In the second half, I will switch to the gauge theory side, following the proposal of Donaldson–Thomas, to discuss G2-instantons and the corresponding moduli space. The lectures are meant to be introductory and accessible to anyone with basic knowledge in Riemannian geometry
