Discretionary services typically refer to professional work and complex service work by physi-cians,software developers,web designers,lawyers,or financial analysts,where there are no standard working processes and customer perceived quality of service increases with the time spent on it.Recently,research on these services,especially the corresponding speed-quality tradeoff problem,has gained more and more attention.This paper reviews both the analytical models and the empirical studies in this area,highlighting their contributions and pointing out potential directions for future research.