  In G2 manifolds, 3-dimensional associative submanifolds (instantons) play a
role similar to J-holomorphic curves in symplectic geometry. In [21],
instantons in G2 manifolds were constructed from regular J-holomorphic curves
in coassociative submanifolds. In this exposition paper, after reviewing the
background of G2 geometry, we explain the main ingredients in the proofs in
[21]. We also construct new examples of instantons.
