The authors established a process for the development and testing of mobile phone-based health interventions that has been implemented in several mHealth interventions developed in New Zealand. This process involves a series of steps: conceptualization, formative research to inform the development, pretesting content, pilot study, pragmatic randomized controlled trial, and further qualitative research to inform improvement or implementation. Several themes underlie the entire process, including the integrity of the underlying behavior change theory, allowing for improvements on the basis of participant feedback, and a focus on implementation from the start. The strengths of this process are the involvement of the target audience in the development stages and the use of rigorous research methods to determine effectiveness. The limitations include the time required and potentially a less formalized and randomized approach than some other processes. This article aims to describe the steps and themes in the mHealth development process, using the examples of a mobile phone video messaging smoking cessation intervention and a mobile phone multimedia messaging depression prevention intervention, to stimulate discussion on these and other potential methods.