This book examines the extent to which product innovations stem from small, young firms versus large, established firms by analysing the patenting behaviour of public firms derived from the NBER-Compustat database and assembling a dataset of private and public firms from the Thomas Register of American Manufacturers. The Thomas Register evidence shows that small firms are surprisingly capable of inventing and managing products relative to large firms. In 2002, small firms had an average of 10.01 products, while large firms had an average of 21.44 products; thus, small firms had on average half the number of products per firm compared to large firms. The NBER-Compustat evidence shows that small firms are more innovative per dollar of R&D than large firms, and the extent to which this occurs is decreasing in firm age; and young firms are more innovative per dollar of R&D than old firms, and the extent to which this occurs is decreasing in firm size.