The authors summarized the literature landscape for longitudinal studies examining the impact of COVID-19 on youth mental health. While some studies show that depression in youth increased during the pandemic, others indicate that mental health experienced some recovery in summer 2020 when some lockdown measures were lifted. Studies investigating youth anxiety, suicidal ideation, and self-harm were also mixed. Studies also reported initial decreases in alcohol and substance use in early 2020 due to fewer social opportunities, whereas longitudinal investigations demonstrated that substance use increased for higher-risk youth. The authors highlight that developed countries have experienced unprecedented increases in eating disorders, including hospitalizations for eating disorders, coinciding with the start of the pandemic. Increases in eating disorders were also reported in the general population and adults. The authors call for more longitudinal monitoring of youth mental health during the pandemic, as well as more evidence to evaluate the effectiveness of online youth mental ehalth services.