What counts as evidence in linguistics? This question is addressed by the contributions to the present volume (originally published as a Special Issue of Studies in Language 28:3 (2004). Focusing on the innateness debate, what is illustrated is how formal and functional approaches to linguistics have different perspectives on linguistic evidence. While special emphasis is paid to the status of typological evidence and universals for the construction of Universal Grammar (UG), this volume also highlights more general issues such as the roles of (non)-standard language and historical evidence. To address the overall topic, the following three guiding questions are raised: What type of evidence can be used for innateness claims (or UG)?; What is the content of such innate features (or UG)?; and, How can UG be used as a theory guiding empirical research? A combination of articles and peer commentaries yields a lively discussion between leading representatives of formal and functional approaches.