Background: With the ubiquity of smartphones, #Digital self-report instruments have enormous potential to support the general population in monitoring their #MentalHealth. A primary challenge for researchers committed to advancing this work is simply to scope the plethora of widely used candidate instruments. The overarching aim of this study was to address this challenge to support and guide future research in this burgeoning area. Objective: This study aimed to conduct a literature review of self-report instruments used in empirical studies to measure #MentalHealth (1) in the general population, (2) delivered in a #Digital format, and (3) in longitudinal designs. Given the wide range of recognized “#MentalHealth” constructs, the review’s search strategies were guided by Keyes’ dual continua model of #MentalHealth, recognizing both deficits- and strengths-based constructs. This study’s primary objective was to develop a first-of-its-kind ranking and synthesis of the most frequently used instruments that are potentially suitable for #MentalHealth self-monitoring. It was not an objective of this study to evaluate psychometric properties of the identified instruments—we hope the present ranking and synthesis will provide the foundation for future research into optimal #Digital, prospective self-report of #MentalHealth. Methods: Five major electronic databases were searched. Studies that administered #Digital #MentalHealth instruments (in English) repeatedly to community dwellers in the general adult population were eligible. The included studies were grouped by instruments for synthesis using a narrative #Approach. Results: Preliminary screening of 95,849 records identified 8460 eligible records, among which 1000 records were randomly selected over 4 iterations for full-text screening. A total of 223 records were included. We found that the top 30 most commonly used instruments accounted for 78.4% (308/393) of the total usage across studies. These instruments predominantly measure deficits-based #MentalHealth constructs. The Patient #Health Questionnaire 9 Items and Generalized #anxiety Disorder 7 Items were by far the most used instruments. The most commonly measured strengths-based constructs were life satisfaction and mental well-being. Conclusions: The findings of this review strongly suggest that scientific investigation of #MentalHealth constructs across time on #Digital platforms still prioritizes deficits-focused instruments originally developed for pen-and-paper administration using classical test theory. These findings are discussed in light of evidence in the literature that deficits-focused instruments demonstrate inferior distributional properties (floor effects) in the general population and theory suggesting that both deficits- and strengths-focused measurements are required to holistically assess #MentalHealth. Limitations of the review include the restricted focus on English language instruments and the pragmatic #Approach to selecting records for full-text screening. It is concluded that, in the smartphone age, it would be timely to develop new #Digital instruments framed by holistic models of #MentalHealth and using contemporary test construction #Approaches. Trial Registration: PROSPERO CRD42022306547; https://www.crd.york.ac.uk/PROSPERO/view/CRD42022306547