The Immersed Interface Method (IIM, LeVeque/Li) was motivated by Peskin's Immersed Boundary (IB) Method. The IIM shares many characteristics of the IB method. Both methods use simple grid structure. The original motivation of the IIM is to improve the accuracy of the IB method from first order to second order. This has been achieved by incorporating the jump conditions into numerical schemes near or on the interface. In this talk, I will summarize some recent advances of the IIM, particularly, the applications to incompressible Stokes and Navier Stokes equations with singular sources, discontinuous viscosity, irregular domains, and free boundary and moving interfaces using the augmented IIM. Applications include flow past cylinders, moving contact line problems, deformable moving interfaces, and incompressible interfaces in incompressible flows. This talk is also an introduction to my (with Dr. Ito) SIAM book: The Immersed Interface Method -- Numerical Solutions of PDEs Involving Interfaces and Irregular Domains.