The 2021 Adaptive and Personalized Persuasive Technology (ADAPPT 2021) workshop is the second edition of the ADAPPT series, which commenced in 2019. It is organized in conjunction with the 29th Association for Computer Machinery (ACM) Conference on User Modeling, Adaptation and Personalization (UMAP). We summarize the main ideas, topics and results of the 10 papers accepted for publication in the adjunct proceedings of the UMAP conference and for video/oral presentation at the virtual workshop.