Engagement as a concept can explain why Digital Health Interventions (DHIs) produce individual variance in outcomes, and sometimes limited effectiveness, especially in practice. However, previous literature on engagement across different domains (e.g., Psychology, Implementation Science, Human-Computer Interaction) yields disparate conceptualizations, research methods, design strategies, and measurement methods. Therefore, this workshop aims to: bring together a diverse group of researchers within the field of DHIs with an interest in engagement; provide an overview of how engagement has been used, in terms of concept, measures, and strategies; work towards a shared understanding of how engagement, with its diverse measures and strategies, can be leveraged to inform the design, development, and evaluation of meaningful DHIs. We welcome submissions either as a description of a use case that includes: how engagement was defined, measured, designed for by our participants, as well as their lessons learned; or as a short position paper describing their interest in the topic, future plans for measuring/designing for engagement, and current challenges. Our post-workshop plans aim to draw from this transdisciplinary collaboration to document lessons learned on how to employ engagement in DHI development, research and design.