The Internet is a highly complex and newly emerged artifact. Building upon and going beyond two previous studies [Yan, Z. (2005). Age differences in children's understanding of complexity of the Internet. Journal of Applied Developmental Psychology, 26, 385-396.; Yan, Z. (2006). What influences children's and adolescents' understanding of the complexity of the Internet? Developmental Psychology, 42, 418-428.], children's and adolescents' understanding of the Internet was assessed and developmental sources of their understanding were analyzed. With 105 adults (M age = 24) as a reference group, 681 9- to 17-year olds were assessed for their understanding of the technical and social complexity of the Internet, and the internal and external developmental sources of their understanding were examined using structural equation modeling. The children and adolescents were found to have (a) limited understanding of the technical and social complexity of the Internet, showing perception-bounded knowledge rather than conceptually correct understanding, and (b) limited resources to develop their understanding, relying predominantly on one domain-general source rather than on various developmental sources of good quality. Developmental pathways of understanding of the Internet as an emergent and complex artifact are described, and implications for implementation of the Children's Internet Protection Act of 2000 are discussed. (Contains 2 figures and 5 tables.)