Large cities make businesses and workers more productive. This is because they benefit from agglomeration economies, which means they do better when they are close together. Evidence shows that this is not just by chance or because of different skills. Wages and rents also show patterns that support this idea. However, we still need to understand more about why this happens. We know that sharing resources and finding the right match between businesses are important factors. But we need to learn more about how cities help us learn and improve. More research is needed to figure out exactly why big cities make us more productive.