Abstract: Thermodynamic non-equilibrium is a defining feature of living systems on all levels of organization. Cells and tissues are built of “active matter”, dynamic materials with built-in force generators. Such materials self-organize in biological systems into well-ordered dynamic steady states, sustained by the dissipation of metabolic energy. We use advanced light microscopy as well as microscopic motion and force-sensing techniques to characterize the complex mechanical properties of and the motion and stress patterns in biological active matter, in particular the actin cortex, both in reconstituted model systems and in cells. I will introduce methods to detect and quantitate thermodynamic non-equilibrium using fundamental concepts of statistical physics such as the fluctuation-dissipation theorem and the principle of detailed balance. Closely related to mechanical activity in biological systems are mechanosensory processes. I will present some recent results we obtained on the chordotonal organs of Drosophila.