Introduction: The international mobility of knowledge workers and the associated brain-drain/brain-gain phenomena have gained prominence in public policy discussions on innovation and economic growth - in both developed and developing economies. Many governments have made efforts to attract skilled migrants from abroad - inciting what may be colloquially called a global competition for talent. This chapter focuses on a special set of knowledge workers, namely, inventors. In particular, we introduce a new database that maps migratory patterns of inventors, extracted from information contained in patent applications filed under the Patent Cooperation Treaty (PCT). In addition to describing this newly constructed database, we provide a descriptive overview of inventor migration patterns around the world. As described in Chapters 1 and 2, the economic importance of high-skilled migration has long been recognized in the literature, even if empirical research on the topic is of more recent vintage. Indeed, advances in our understanding of the effects of skilled worker migration to a significant extent have been due to new data becoming available over the last fifteen years. In particular, the pioneering study by Carrington and Detragiache (1998) represents the first systematic attempt to construct a comprehensive data set on emigration rates by educational attainment. Their study provides 1990 emigration rates for sixty-one sending countries to countries of the Organization for Economic Cooperation and Development (OECD). They estimate skill levels by extrapolating the schooling levels of US immigrants by origin country to other receiving countries. Since then, other macro approaches have followed, including that of Docquier and Marfouk (2006), who estimate immigrant stocks in thirty OECD countries for 174 origin countries for 1990 and 2000, and Defoort (2008), who extends this work by providing immigrant stocks by schooling level for five-year intervals from 1975 to 2000, but only to six OECD destination countries. Docquier et al. (2009) provide a gender breakdown, and Beine et al. (2007) provide data broken down by the entry age of immigrants.Read less <