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In this presentation, we review historical and modern results on the linear response of dynamical systems to external perturbations and the celebrated relationship between fluctuations and dissipation expressed by the Fluctuation-Dissipation Theorem (FDT). The conceptual derivation of FDT originated from the definition of the equilibrium state and Onsager’s regression hypothesis. Over time the fluctuation-dissipation relation was vividly investigated for systems away from equilibrium, frequently exhibiting wild fluctuations of measured parameters. In this talk, we recall the major formulations of the FDT, such as those proposed by Langevin, Onsager, and Kubo [1]. We discuss as well the importance of fluctuations in a wide class of growth phenomena. We point out challenges and opportunities where the relationship breaks down and cannot be adapted.[1] F. A. Oliveira, R. M. S. Ferreira, L. C. Lapas and M.H. Vainstein, Review article Anomalous Diffusion: A Basic Mechanism for the Evolution of Inhomogeneous Systems Frontiers in Physics, 7, (18) (2019).