Background: Attention-Deficit/ Hyperactivity Disorder (ADHD) is a prevalent condition in children and adolescents. Although there are pharmacological and non-pharmacological treatments for this disorder, barriers in accessing evidence-based treatments are still a major problem. Digital health interventions are promising for multiple mental health problems. Recent years have brought an increase in the number of existing mobile apps designed for the management of ADHD. The aim of this study was to systematically review the existing mobile apps designed for ADHD in terms of general characteristics, empirical support for their development and efficacy/ effectiveness, and to describe the content and design of the four most downloaded ADHD apps. Method: We conducted systematic searches on iTunes/iOS (Apple App Store), Google Play and the National Health Service Health Apps Library up to May 2017 and checked for changes in March and September 2019. We included those apps that were designed for ADHD, target assessment, treatment, or both, were in English and were functional. We identified 355 apps in the virtual stores, out of which we included 109 apps in the present systematic review. For each app we extracted the following information: target population, developer, price, number of downloads, ratings, privacy, available language other than English, category, purpose and empirical support. A second search was conducted in literature databases up to September 2019: PsycINFO, Pubmed, Scopus, Web of Science, Cochrane database. Results: We found 109 ADHD apps in the virtual stores available to both young and adult populations, developed for children, adolescents, parents, teachers, and professionals. Most of the apps included are designed for treatment, or ADHD symptoms assessment, however, we found several apps designed for both assessment and treatment purposes. Very few apps contained information regarding their development and none contained information regarding evidence for its efficacy/ effectiveness. Four apps were the most downloaded, with 10,000 (three apps) to 100,000-500,000 (one app) downloads. Out of 51 papers identified through systematic searches in the literature, we identified only one study that met our inclusion criteria, however, this study was published in 2018, outside of the 2017 app store search, therefore, there is no overlap between evidence in the literature and apps on the market. Conclusions: Given the large proliferation of mental health apps and their potential benefits in terms of dissemination and costs, future research needs to be conducted in order to establish the safety and efficacy of ADHD apps available on the commercial market.