Recent years have seen an impressive increase in web-based research, of which we review and discuss two main types. First, researchers can create online versions of traditional questionnaires. Using the internet in this way usually does not compromise the psychometric properties of such measures, and participants are typically not less representative of the general population than those of traditional studies. Technical guidelines are provided to set up such studies, and thorny issues such as participants' anonymity are discussed. We will also discuss issues regarding the assessment of minors and the repeated assessment of participants to assess developmental changes via the web. Second, the internet has changed the way people interact with each other. The study of the psychosocial consequences of this development is called cyberpsychology. We review emerging findings from this young discipline, with a focus on developmentally-relevant implications such as the use of the internet by adolescents to disclose personal information. (Contains 1 table.)