The book addresses a controversial current topic in language acquisition studies: the impact of frequency on linguistic structure in child language. A major strength of the book is that the role of input frequency in the acquisition process is evaluated in a large variety of languages, topics and the two major theoretical frameworks: UG-based and usage-based accounts. While most papers report a clear frequency effect, different factors that may be interacting with pure statistical effects are critically assessed. An introductory statement is made by Thomas Roeper who calls for caution as...