Did you like that or not? Did the system’s choice of adaptation aggravate you more, or did it bring about an expression of gratefulness? Does this interest you or bore you? Recognition of the effects an action has on a user is a key part of adapting successfully to users; how can machines be enabled to recognize affective expressions such as frustration, interest, anger, or joy? And, what are guidelines for designing their response, especially given that recognition is likely to not be perfect? This talk will present new technologies under development for sensing and responding appropriately to human affective expressions. Current applications include usability feedback, health behavior change, learning companions, and human-robot interaction.