The 3 volume-set LNCS 11566, 11567 + 11568 constitutes the refereed proceedings of the Human Computer Interaction thematic area of the 21st International Conference on Human-Computer Interaction, HCII 2019, which took place in Orlando, Florida, USA, in July 2019. A total of 1274 papers and 209 posters have been accepted for publication in the HCII 2019 proceedings from a total of 5029 submissions. The 125 papers included in this HCI 2019 proceedings were organized in topical sections as follows: Part I: design and evaluation methods and tools; redefining the human in HCI; emotional design, Kansei and aesthetics in HCI; and narrative, storytelling, discourse and dialogue. Part II: mobile interaction; facial expressions and emotions recognition; eye-gaze, gesture and motion-based interaction; and interaction in virtual and augmented reality. Part III: design for social challenges; design for culture and entertainment; design for intelligent urban environments; and design and evaluation case studies.