Abstract: The rapid development of web technology has promoted the emergence and organization of the collaborative Wiki systems. This paper introduces the Wikipedia's history, macro-level statistical properties, evolution regularities, and so on. Especially the application of the motivation and methods of complex network study in analyzing the Wikipedia is emphasized. Wikipedia's significance and impacts on society, economy, culture and education are also discussed. Finally, some open questions are outlined for future research; especially the connection between Wikipedia and the new development in complexity sciences, such as the studies of complex network and human dynamics.