The importance of crispness and crunchiness as textural descriptors was illustrated in A. S. Szczesniak and D. H. Kleyn's study of consumer awareness of food texture. The importance and desirability of the qualities crispness and crunchiness have suggested the need to define and measure them. Over the years, many scientists have worked towards this goal. This chapter examines some of these studies, focusing primarily on the sensory perceptions of crispness and crunchiness, but also highlighting some of the more effective instrumental measurements of these qualities. Food scientists have changed from viewing crispness as a rheological property of foods to viewing it as a perception involving both tactile and auditory components. However, the relative roles of rheological and acoustical properties in the perception of crispness have yet to be determined. Correlations between oral crispness judgments and the instrumental sensory parameters were generally considerably lower than correlations between auditory crispness judgments and instrumental parameters.