The objective of this article is to aid clinicians in understanding the current state of the development and application of quality of life (QOL) instruments as outcome measures in cancer clinical research and practice. As a result of the achievements of the past two decades, the concept of QOL has been defined and many reliable and valid measurement tools have been developed. The two main approaches to QOL assessment, psychometric-based and utility-based, are discussed together with a brief description of the strategies for meaningful interpretation of QOL profiles. QOL measures in oncology have the potential to be used to study populations in randomised clinical trials, to aid patient-clinician interactions in routine practice and to support policy decision making and economic evaluation of healthcare provision.