We use administrative data linking workers and firms to study employer-to-employer (E-to-E) flows. After discussing how to identify such flows in quarterly data, we investigate their basic empirical patterns. We find that the pace of E-to-E flows is high, representing approximately 4% of employment and 30% of separations each quarter. The pace of E-to-E flows appears to be highly procyclical and varies systematically across worker, job, and employer characteristics. There are rich patterns in terms of origin and destination of industries. Somewhat surprisingly, we find that more than half of the workers making E-to-E transitions switch even broadly defined industries (i.e., NAICS supersectors).