Background: This study aimed to develop and evaluate the effectiveness of two web-based decision aids designed to help parents of children aged 10–17 years and young adults aged 18–26 years make informed decisions about the HPV vaccine. Methods: The decision aids were developed according to the International Patient Decision Aid Standards (IPDAS) criteria and included information about the vaccine, probabilities of benefits and side effects, personal narratives, and values clarification. The study utilized a quasi-experimental design and included 120 Hebrew-speaking parents and 160 young adults. Participants completed baseline surveys and, two weeks after using the decision aid, completed a follow-up survey. Results: Both parents and young adults experienced a reduction in decisional conflict, an increase in self-efficacy, and greater confidence in the safety and effectiveness of the vaccine. The proportion of participating parents deciding to vaccinate their children against HPV increased from 46% to 75%, and the proportion of participating young adults leaning towards receiving the HPV vaccine increased from 64% to 92%. Conclusions: The study highlights the importance of using decision aids to support informed decision making about vaccination and suggests that web-based decision aids may be a useful tool for supporting Israeli parents and young adults to make HPV vaccination decisions.