In my talk I will present two recent works focused on the perfect absorption and transmission of waves through interferometric cancellation of backscattering. In the first case [1], we demonstrate that even a weakly absorbing film can be turned into a “coherent perfect absorber” by building a degenerate cavity around it. This special cavity perfectly couples incoming light fields with arbitrary wavefronts into the absorber – even for the case that light is a dynamically varying speckle pattern. In the second case [2], we demonstrate how to construct an anti-reflection structure for a complex scattering system like a disordered medium. Similar to an anti-reflection coating for conventional eye-glasses, this structure leads to perfect transmission across the scattering system by suppressing back-scattering for any incoming wavefront. If time permits, I will also say a few words about the topological origin of the above effects and how this aspect can be used to engineer thermal radiation [3]. [1] Y. Slobodkin, G. Weinberg, H. Hörner, K. Pichler, S. Rotter, and O. Katz, Science 377, 995 (2022) [2] M. Horodynski, M. Kühmayer, C. Ferise, S. Rotter, and M. Davy, Nature 607, 281 (2022) [3] M. S. Ergoktas, A. Kecebas, K. Despotelis, S. Soleymani, G. Bakan, A. Kocabas, A. Principi, S. Rotter, S. K. Özdemir, and C. Kocabas, arXiv:2401.08316