Cancer-related fatigue (CRF) is a highly prevalent and debilitating symptom experienced by most cancer patients during, and often for considerable periods after, treatment. The recognition of the importance of CRF to patients' psychosocial and cognitive functioning, as well as to their quality of life, has driven the development of a wide range of assessment tools for screening and diagnosis of CRF. Over 20 different measures have been used to assess CRF from either a unidimensional or multi-dimensional perspective. Unidimensional measures are often single-question scales that generally focus on identifying the occurrence and severity of CRF, whereas multidimensional measures may also examine the effect of CRF across several domains of physical, socio-emotional, and cognitive functioning. This paper provides an overview and critique of measures commonly used to assess CRF. Single-question assessment is the most commonly used and the most useful methodology. Strategies to facilitate reliable assessment of CRF are also discussed. Disclosure of potential conflicts of interest is found at the end of this article.