This paper, authored by a team of experts, provides an overview of current research on engagement with digital behavior change interventions (DBCIs) and identifies key issues and future research directions. The authors reflect on current approaches to conceptualizing and measuring engagement, emphasizing the need to understand the relationship between engagement with the digital intervention and the desired behavior change. They argue that "effective engagement" should be defined as sufficient engagement to achieve intended outcomes, rather than simply more engagement. The paper discusses methods for assessing different aspects of engagement, highlighting the importance of identifying valid and efficient combinations of measures to develop and test multidimensional models of engagement. It also explores how interventions can be designed to fit the user's specific needs and context, emphasizing the need for a user-centered and iterative approach to development. The authors conclude by discussing techniques for promoting effective engagement, including tailoring interventions to individual needs and combining DBCIs with human support. They highlight the importance of involving users in intervention development and the potential benefits of integrating human facilitation with digital interventions.This paper, authored by a team of experts, provides an overview of current research on engagement with digital behavior change interventions (DBCIs) and identifies key issues and future research directions. The authors reflect on current approaches to conceptualizing and measuring engagement, emphasizing the need to understand the relationship between engagement with the digital intervention and the desired behavior change. They argue that "effective engagement" should be defined as sufficient engagement to achieve intended outcomes, rather than simply more engagement. The paper discusses methods for assessing different aspects of engagement, highlighting the importance of identifying valid and efficient combinations of measures to develop and test multidimensional models of engagement. It also explores how interventions can be designed to fit the user's specific needs and context, emphasizing the need for a user-centered and iterative approach to development. The authors conclude by discussing techniques for promoting effective engagement, including tailoring interventions to individual needs and combining DBCIs with human support. They highlight the importance of involving users in intervention development and the potential benefits of integrating human facilitation with digital interventions.