Family nursing researchers are charged with addressing the conceptual and methodological underpinnings of family research when developing family-focused interventions. Step-by-step guidance is needed that integrates current science of intervention development with family science and helps researchers progress from foundational work to experimental work with policy integration. The purpose of this manuscript is to provide pragmatic, evidence-based guidance for advancing family intervention research from foundational work through efficacy testing. Guidance regarding the development of family interventions is presented using the first three of Sidani’s five-stage method: (a) foundational work to understand the problem targeted for change; (b) intervention development and assessment of acceptability and feasibility; and (c) efficacy testing. Each stage of family intervention development is described in terms of process, design considerations, and policy and practice implications. Examples are included to emphasize the family lens. This manuscript provides guidance to family scientists for intervention development and implementation to advance family nursing science and inform policy.