Sex offenders can view child pornography and communicate with potential victims and other offenders in minutes through the Internet. The anonymity of cyberspace further complicates the situation. Police who decide to undertake proactive Internet Crimes Against Children (ICAC) investigations need to understand that effective law enforcement always begins with common sense augmented by training and experience. Online investigators need to understand the nature and attitudes of sex offenders. Online investigations usually focus on the distribution of child pornography and on online solicitation of children for sex, as well as meetings with children for the purposes of sex. Proactive law enforcement must begin with sound undercover practices. Investigators who present themselves as children must take extra care to present appropriate victim profiles. The online investigator must also use believable proactive techniques. Illustrations