The essays in part I show that resistance to and non-use of a technology can be a crucial factor in the eventual modification and improvement of that technology; examples considered include the introduction of the telephone into rural America and the influence of non-users of the Internet. The essays in part II look at advocacy groups and the many kinds of users they represent, particularly in the context of health care and clinical testing. The essays in part III examine the role of users in different phases of the design, testing, and selling of technology. Included here is an enlightening account of one company's design process for men's and women's shavers, which resulted in a "Ladyshave" for users assumed to be technophobes. Taken together, the essays in How Users Matter show that any understanding of users must take into consideration the multiplicity of roles they play--and that the conventional distinction between users and producers is largely artificial.