We examine the politics of US state and federal policy supporting wind and solar in the electricity sector and biofuels and electric vehicles in the transportation sector. For each technology, we provide two policy case studies: the federal Production Tax Credit (PTC) and state Renewable Portfolio Standards (RPS) for wind; state Net Energy Metering (NEM) and the federal investment tax credit (ITC) for solar; federal excise tax incentives and the Renewable Fuel Standard (RFS) for biofuels; and California's Zero Emission Vehicle (ZEV) mandate and federal tax incentives for electric, vehicles. Each case study traces the enactment and later revision of the policy, typically over a period of twenty-five years. We use these eight longitudinal case studies to identify common patterns in the politics of US renewable energy policy. Although electricity and transportation involve different actors and technologies, we find similar patterns across these sectors: immature technology is underestimated or misunderstood; large energy bills provide windows of opportunity for enactment; once enacted, policies are extended incrementally; there is increasing politicization as mature technology threatens incumbents.