The acousto-ultrasonic technique was devised to assess diffuse flaw populations and any associated changes of the mechanical properties of composites and composite- like materials. Acousto-ultrasonics has been used to evaluate fiber reinforced composites, adhesive bonds, paper and wood products, cable and rope, and also human bone. The potentials and limitations of the technique are reviewed. Basic methods and quidelines are discussed. The underlying hypothesis for acousto ultrasonic materials evaluation is stated and needs for theory and signal analysis development are indicated.