As with other online communities, it is important to design elements of citizen inquiry projects that will attract and engage members. This chapter describes the process of designing an online community for citizen inquiry. It builds on design principles of inquiry learning, citizen inquiry and other online communities. The ‘Weather-it’ citizen inquiry community is intended to engage and support people in initiating and joining sustainable citizen-led investigations. The findings indicate some successful mechanisms for the design of effective and sustainable citizen inquiry communities and ways to sustain them.