This chapter reviews methylphenidate misuse, abuse, dependence, diversion, and malingering associated with its use as a prescription medication for attention-deficit/hyperactivity disorder and the nonmedical use linked to its stimulant effects. Methylphenidate-induced regional elevations in brain dopamine appear to be integral to both efficacy in attention-deficit/hyperactivity disorder and potential for abuse, raising potential concerns for drug safety and prescription drug diversion costs associated with nonmedical use. Regardless, methylphenidate is an important treatment option, and detecting malingering for the purpose of illicit access to methylphenidate for subsequent misuse or diversion is a difficult challenge. Also discussed are the effects of methylphenidate in patients with comorbid substance use disorder and the potential linkage of methylphenidate use with subsequent substance abuse. The current data suggest that methylphenidate misuse and diversion are common health-care problems with a stimulant prescription drug diversion prevalence of approximately 5-10 % of high school students and 5-35 % of college students. The effectiveness and speed of action of methylphenidate are deemed desirable to enhance attention and focus performance for activities such as studying for exams, but methylphenidate is also misused recreationally. These data suggest a need for close screening and therapeutic monitoring of methylphenidate use in the treatment of attention-deficit/hyperactivity disorder.