This dissertation studies the relationship between immigration and innovation. It adopts an empirical perspective and focuses on Switzerland, combining the use of patent data and immigration administrative records. The first essay is based on a novel database on immigrant inventors and explores their role in Swiss R\&D activities, their productivity, and inventive career before and after immigration. It shows that highly productive inventors are over-represented among immigrants and that foreign inventors tend to enter Switzerland early in their careers and with little prior inventive experience. The second essay studies the innovation effects of the Agreement on the Free Movement of Persons (AFMP), which lifted immigration restrictions for EU citizens to Switzerland after its introduction in 2002. It exploits a natural experiment generated by regional differences in the exposure to the AFMP and influx of foreign workers. It finds that the AFMP introduction increased regional patenting in Switzerland and did not depress the inventive output of its neighbouring countries. In addition, Swiss inventors did not reduce their inventive activity due to newly arrived foreigners. Further results show that the AFMP had a positive effect on incumbent inventors' productivity, increasing the number of foreign collaborators and the variety of technical knowledge available. The third essay also focuses on the AFMP and studies the effects of the Swiss and the German labor markets' integration on technical knowledge diffusion. Using patent citation data and textual similarity measures, it demonstrates that the abolition of immigration restrictions for commuters residing in the German state of Baden-Wuerttemberg and working in Switzerland increased the diffusion of German inventions patented in commuters' residential locations into Switzerland.