In recent years, outcome assessment following different therapeutic procedures has increasingly focused on the patient's perspective. While traditional measures of outcome, including physical examination and imaging diagnostics of the knee are complementary, patient-relevant questionnaires have become more and more important in determining the value of therapeutic procedures. Therefore, there is a clear need for clinicians in all fields, especially orthopedics, to be familiar with the available scoring systems and their relative strengths and weaknesses. Several questionnaires are now available for active patients with knee disorders, as well as for older patients with degenerative conditions. We thus present knee rating scales, patient-reevant questionnaires, and generic measurement tools available for the assessment of patients with osteoarthritis following knee injury. These tools are described in detail and their relative merits are discussed. Since the reliability, validity and responsiveness of the knee scales are crucial for their use as outcome measures, these parameters are also described precisely. Along with the growing number of international, multi-cultural, and multilingual research projects, there is a need to adjust measurement tools to different conditions and circumstances. There is general agreement that a questionnaire, when adapted for use in a new country, should not only be translated precisely, but also adjusted culturally to maintain the content validity of the original version. The process of cross-cultural and linguistic adaptation includes initial translation, translation synthesis, back translation, review by an expert committee, testing of the pre-final version and, finally, the validation study. This procedure is described in detail.