Objective: The aim of this study is to illustrate an evidence-based and theoretically informed mhealth resource (smartphone app) designed to provide communication support for informal cancer caregivers (friends or family members). Methods: An eight-step process was conducted: (a) review of existing print resources, (b) selection of theoretical framework for content development, (c) integration of stakeholder feedback and literacy assessment into an alpha print model, (d) review of existing mhealth resources, (e) development of prototype, (f) assessment of caregiver acceptability (n = 5), (g) assessment of quality and perceived impact by cancer providers (n = 26), and (h) acceptability testing with caregivers (n = 6). Results: Key stakeholders were integrated throughout development and user testing of this iOS smartphone app. The smartphone app consists of talking tips and resources for caregiver communication with the patient, family, far away family, and health care providers, as well as general information sharing features. Conclusions: This study demonstrates feasibility and development of an evidence-based and theory-driven mhealth resource to support caregiver communication about cancer. This is the first theory-driven mhealth application created to support the communication burden experienced by cancer caregivers. A larger study is needed to establish the efficacy of the app as an intervention for caregivers.