This article describes the development of the Adult Sensory Processing Scale (ASPS), a sensory processing questionnaire for adults. The ASPS measures self-reported responses to input from distinct sensory systems and is intended to be sensitive to individual differences in the adult population. ASPS construction involved two phases: item development and instrument construction. During item development, content validity of 71 items was assessed by means of expert ratings. During instrument construction, items were evaluated using data from an online survey of 491 adults. Exploratory factor analysis and Rasch analysis yielded an optimal solution of eight factors representing vestibular overresponsiveness, auditory overresponsiveness, visual overresponsiveness, social tactile overresponsiveness, proprioceptive seeking, general underresponsiveness, vestibular–proprioceptive underresponsiveness affecting postural control, and vestibular overresponsiveness–intolerance to movement. The final ASPS contains 39 items and demonstrates acceptable internal consistency, strong content validity, and adequate construct validity.