Innovation has become a key factor for economic growth, but how does the process take place at the level of individual firms? This book looks at the main results of the OECD Innovation Microdata Project -- the first large-scale effort to exploit firm-level data from innovation surveys across 20 countries in an internationally harmonised way, with a view to addressing common analytical questions. Through the use of common indicators and econometric modeling, this analytical report presents a broad overview of how firms innovate in different countries, highlights some of the limitations of current innovation surveys, and identifies directions for future research.