Despite being used commonly in sleep medicine, the term "sleep quality" has not been rigorously defined. The purpose of this article is to consider objective measures of the subjective "sleep quality" experience. In order to do so, it was necessary to choose a definition of "sleep quality" as a basis for discussion. We have chosen to employ the simple Likert-style rating of (the previous night's) sleep quality, commonly included as an item on sleep diaries, as the core sleep quality indicator and focus of this article. The potential objective measures discussed include polysomnography, cyclic alternating pattern and actigraphy. We review the strengths and weaknesses of these measures as well as discuss challenges facing the development of an objective correlate of "sleep quality" ratings, including that such ratings may reflect non-sleep phenomena such as mood or health status and the possibility that "sleep quality" may reflect different aspects of sleep among people. We also discuss new approaches intended to address these challenges, including: (1) combining different types of measures; (2) sub-grouping individuals based on clinical or physiological characteristics and developing different measures in these subgroups; and (3) sub-grouping based on the association of potential measures and quality ratings over nights.