Inadequately or poorly designed environments and tools of daily living impose barriers to people with a disability. This issue needs to be addressed in order for people with disabilities to lead full and purposeful lives. To accomplish this goal it is imperative that designers of environments and artifacts have an in-depth knowledge of human functioning in the performance of tasks and problem-solving strategies to develop environments and products that best accommodate performance of these tasks. They require an understanding and useful characterizations of the abilities of people with disabilities and relevant mechanisms to incorporate this into a modern design process.