Sweetened beverage (SB) taxes have recently been introduced to prevent obesity by several governments, but limited information on related policy adoption processes hampers further diffusion. We investigated the agenda-setting and decision-making phases of SB tax reforms in Berkeley and Philadelphia (where it was successfully adopted), and Cook County (where it was repealed). A web-based survey, semi structured stakeholder interviews, and a local media coverage analysis were used to collect information. Findings were structured and analyzed using the health policy triangle of Buse, Mays and Walt. Six general lessons emerged. First, the policy was coupled to existing high-agenda items (e.g., financing pre-kindergarten in Philadelphia). Second, policy framing had to align prevailing political sentiments, as expressed in media (e.g., ‘Berkeley vs. Big Soda’ echoed skepticism of corporate influence in politics). Third, existing tax policies and political decision-making rules were important (e.g., confusion how the SB tax related to state and federal taxes fueled Cook County opposition). Fourth, the tax structure required technical and political considerations during policy formulation (e.g., artificially-sweetened beverages were included in Philadelphia to counteract arguments that the tax was regressive). Fifth, it was important to build an advocacy coalition upfront (e.g., the Berkeley coalition was constructed prior to announcing the attempt). Sixth, successful advocacy coalitions were locally grounded and influenced local media (e.g., the Cook County opposition engaged local retailers).