The Four Approaches to Interaction Design

User-centered Design: This is the most popular design approach. It focuses on the user's needs and goals. Users are included in every step of the design process. The design is made for the user. An example is a laptop computer.

Activity-centered Design: This approach focuses on the tasks and activities that need to be accomplished. An example is a toaster.

Systems Design: This design approach focuses on the components of a system. It needs "requisite variety", or an assortment of responses to deal with a range of situations, in order to function correctly. An example of this is a wireless printer.
 
Genius Design: This approach is the easiest to use when designing, but can also have a bad turn out. It uses the skill and wisdom of the designer to make products. An example would be the IPhone (because Apple hardly uses any user testing).