Crowdsourcing is a powerful approach to solve some of the biggest problems today - social and scientific. To harness the potential of crowdsourcing, researchers have often relied and successfully used crowd marketplaces such as Amazon Mechanical Turk. However, in spite of a large worker base and past successes, these platforms come with their own limitations. 40% of all the tasks are spam on Mechanical Turk; and it’s also difficult to accomplish tasks which require a broader participation base, or expert knowledge. Citizen crowd, at the same time, involves distributed group of people with diverse background and skills; who might organize to accomplish tasks or solve problems without engaging with paid crowd platforms. The motivation for them lies in reasons other than micro-payments.

In this dissertation, I explore problems of varying size and duration, where mobilizing the citizen crowd can achieve worthwhile goals. To investigate the possibilities with citizen crowdsourcing, I built systems and ran initiatives that require different level of expertise. This thesis highlights three projects, ranging from seconds of micro contributions to months of highly intellectual contributions. To begin with, we built a mobile lock screen application, that supports completion of quick microtasks in short bursts of time - each time someone unlocks their phone. Next, we launched first of its kind large scale distributed and time-critical campaign in India; where we mobilized the crowd and studied aspects around team building, collaboration, incentives and communication channel; to achieve a common goal. Finally, we ran a first of its kind "research-at-scale" initiative, that explores the possibility of crowdsourcing large open ended problems - by connecting professors with students from around the world - providing access and educational value. All these initiatives have engaged thousands of people from around the world, and we can conclude that it is possible to mobilize the citizen crowd to accomplish worthy goals.