SEL2021 thematic school will constitute one of the sessions of the International School "Sound and Light", and will be devoted to nanophononics, the study - most often by optical methods, hence the name "Sound and Light" given to the series of schools – of acoustic waves in systems with a nanometric dimension or structure or even strong local heterogeneity. In 2021, an important place will be given to the study and imaging of viscoelastic biological objects by Brillouin scattering, Raman scattering and impulse methods, in close relation with the COST "BioBrillouin" (https://www.biobrillouin.eu/).