August 11, 2015: China unexpectedly devalues the yuan by 2 percent and signals more devaluation is coming. Within days, equity markets globally are down 5 to 10 percent, volatility spikes, and credit spreads widen. This episode traces how a single currency move becomes a contagion event across asset classes and geographies. The geopolitical and economic context: China's growth is slowing, exports are struggling, and the government wants a weaker currency to boost competitiveness. But the real story is about what the devaluation signaled to global markets about China's economic trajectory and policy priorities. We start with the mechanism: China's currency peg to the dollar had been gradually appreciating in real terms because the yuan was locked in place while the dollar strengthened. The devaluation was a policy choice, but the market interpreted it as a sign that China's economic situation was worse than the government had admitted. We examine the causal chain: a weaker yuan means Chinese exports become cheaper (good for China), but it also means Chinese assets become less attractive (bad for global investors holding yuan-denominated debt), and it signals that the government is willing to use currency devaluation as a policy tool (which makes investors nervous about what else it might do). The conversation lands on the step most investors got wrong: they thought the devaluation was about trade competitiveness, when it was actually a signal about regime confidence. If the government was comfortable devaluing the currency, what else was it hiding? The episode maps the global contagion: why commodity exporters got hit hardest (because a weaker yuan meant weaker demand from China), why emerging market currencies weakened in sympathy (because investors were suddenly nervous about all EM central banks), and why US equity markets sold off (because investors were recalculating global growth assumptions). We close by examining what the devaluation actually accomplished: did it boost exports sustainably, or did it just trigger a round of tit-for-tat currency weakness across other countries?