Publisher Summary This chapter focuses on thermoacoustics. All acoustics in gases in which diffusive effects are considered, belongs to the field of thermoacoustics. However, a practical classification offers itself since the creation of the theory of thermoacoustics in this general sense by Kirchhoff in 1868. The two important results deduced by Kirchhoff from his theory were corrections to the theory of friction; one result corrected Stokes' formula for the sound attenuation of plane waves in an unlimited medium, the second gave a modified result of the Helmholtz–Rayleigh theory of the attenuation in a duct. This chapter discusses thermoacoustic effects caused by heated surfaces, with particular emphasis on situations in which large amplitude acoustic oscillations are maintained. These are caused, as known, by configurations that are unstable. This chapter discusses oscillating flow over a nonisothermal surface. Damping and excitation of a gas column with temperature stratification is discussed. The chapter also elaborates about thermoacoustic streaming in detail.