English: Wikipedia communities are continually innovating ways to attract and retain new editors, but it is hard to know which of these many efforts are most effective. CivilServant works collaboratively with online communities to test tools and innovations aimed at achieving the goals community members care about most. This talk gives a brief introduction to Citizen Behavioral Science, a collaborative process for designing experiments with community consent, and presents two study designs developed with Wikipedians; a project with French Wikipedia to test the effectiveness of their Welcome Message and a project with Arabic, German, Persian and Polish Wikipedias that tests the effects of receiving Thanks on newcomer retention. The results of these studies will not be complete by Wikimania (one study will already be fielded and the other at the cusp of being fielded), but we hope that presenting the study designs will give participants ideas about how they can test innovations in their communities.