Personalized Trials, commonly referred to as N-of-1 trials in the published literature, belong to the family of Single Case Designs that have been widely used in psychology, education, and social work. Personalized Trials is a specific form of randomized or balanced designs characterized by periodic switching from active treatment to placebo or between active treatments (also known as multiple crossover or “withdrawal-reversal” designs). The experiments are designed to determine the relative benefits and harms of the candidate treatments for that one patient. In typical Personalized Trials, an individual is assigned to receive a sequence of treatments, often in a random order. For example, a patient might receive treatment A for 2 weeks, followed by treatment B for 2 weeks, and then treatment A again for 2 weeks, based on a random sequence of treatments A and B. Often, neither the patient nor the clinician knows which treatment that patient is receiving. Throughout the trial, the patient closely monitors the effects of the treatments. At the end of the trial, the treatment “code” is broken, the patient and clinician jointly review the results to see if the patient did better with A or B, and they then decide which one(s) would be best for that patient. By prescribing multiple episodes of treatment, Personalized Trials increases the precision of measurement and control for treatment-by-time interactions, that is, the possibility that the relative effects of two treatments vary over time.