Book excerpt: The three-volume set CCIS 1032, CCIS 1033, and CCIS 1034 contains the extended abstracts of the posters presented during the 21st International Conference on Human-Computer Interaction, HCII 2019, which took place in Orlando, Florida, in July 2019.The total of 1274 papers and 209 posters included in the 35 HCII 2019 proceedings volumes was carefully reviewed and selected from 5029 submissions. The 208 papers presented in these three volumes are organized in topical sections as follows: Part I: design, development and evaluation methods and technique; multimodal Interaction; security and trust; accessibility and universal access; design and user experience case studies. Part II:interacting with games; human robot interaction; AI and machine learning in HCI; physiological measuring; object, motion and activity recognition; virtual and augmented reality; intelligent interactive environments. Part III: new trends in social media; HCI in business; learning technologies; HCI in transport and autonomous driving; HCI for health and well-being.