Forgetting is in common in daily life, and 50-80% everyday's forgetting is due to prospective memory failures, which have significant impacts on our life. More seriously, some of these memory lapses can bring fatal consequences such as forgetting a sleeping infant in the back seat of a car. People tend to use various techniques to improve their prospective memory performance. Setting up a reminder is one of the most important techniques. The existing studies provide evidences in support of using reminders to cope with prospective memory failures. However, people are not satisfied with existing reminders because of their limitations in different aspects including reliability, optimization, and adaption. Through analysing the functions and features of existing reminder systems, this book draft summarizes their advantages and limitations. We are motivated to improve the performance of reminder systems. For the improvements, the relevant theories and mechanisms of prospective memory from psychology must be complied with, incorporated, and applied in this new study. Based on the literature review, a new reminder model is proposed, which includes a novel reminder planer, a prospective memory based agent, and a personalized user model. The reminder planer is responsible for determining the optimal reminder plan (including the optimal number of reminders, the optimal reminding schedule and the optimal reminding way). The prospective memory agent is responsible for executing the reminding processes. The personalized user model is proposed to learn from users' behaviors and preferences based on human-system interactions and is responsible for adapting the reminder plan to meet users' preferences as much as possible.