Mesoscopic wave physics underpins many of the new developments in ultrasonic spectroscopy for probing the physical properties of complex heterogeneous materials. In this paper, two examples of recent progress are summarized. The first is Diffusing Acoustic Wave Spectroscopy (DAWS), which is a powerful approach for investigating the dynamics of strongly scattering media, one example being velocity fluctuations in fluidized suspensions of particles. Recent advances in using phase statistics to probe the particle dynamics are shown to give increased sensitivity in some situations; this work has also led to new insights into the meaning of phase for multiply scattered waves. The second topic is the spectroscopy of soft food biomaterials, illustrated by experimental studies of ultrasonic velocity and attenuation in bread dough. Since wheat flour dough contains one of the strongest scatterers of ultrasonic waves (bubbles) dispersed in a viscoelastic matrix that is also very dissipative, appropriate ultrasonic techniques provide an excellent means for investigating its structure and dynamics. In addition to fundamental studies, unraveling the contributions of bubbles and matrix to dough properties is relevant to the baking industry, because the bubbles ultimately grow into the voids that determine the structural integrity of bread — an important quality attribute. The interpretation of ultrasonic experiments on bread dough over three decades in frequency is giving new insights into this complex material, as well as providing the basis for new non-destructive methods of evaluating both dough processing behaviour and the breadmaking potential of different flours.