Multi-instantons and gauge/string theory dynamics

The ADHM construction of Yang-Mills instantons can be very naturally understood in the framework of D-brane dynamics in string theory. In this point-of-view, the mysterious auxiliary symmetry of the ADHM construction arises as a gauge symmetry and the instantons are modified at short distances where string effects become important. By decoupling the stringy effects, one can recover all the instanton formalism, including the all-important volume from on the instanton moduli space. We describe applications of the instanton calculus to the AdS/CFT correspondence and higher derivative terms in the D3-brane effective action. (author)