Abstract : Between 2009 and 2012, 10 submarine fiber-optic cables brought high-speed internet to Sub-Saharan Africa, connecting 218 million people and increasing the continent’s bandwidth capacity tenfold. I exploit the staggered rollout of submarine cables and terrestrial backbones as a natural experiment to estimate the economic returns to modern broadband infrastructure. Combining satellite-derived GDP estimates, household surveys, and individual-level data across twelve countries, I find that broadband access raises local GDP by about 1.4 percent per year, increases household consumption, and expands non-farm employment. Effects build gradually over time and are highly spatially localized, decaying sharply beyond 10 kilometers of fiber backbones. Importantly, I document strong complementarities with physical infrastructure: broadband effects on GDP are 50 to 75 percent larger in areas with better road access, suggesting that digital infrastructure amplifies economic growth only when paired with complementary investments in transport infrastructure. Overall, the results highlight that connectivity alone is insufficient to drive structural transformation in low-income settings.