Recent research highlights that patient engagement, conceived as a patient's behavioral, cognitive and emotional commitment to his own care management, is a key issue while implementing new technologies in the healthcare process. Indeed, eHealth interventions may systematically fail when the patient's subjective experience has not been taken into consideration since the first steps of the technology design. In the present contribution, we argue that such an issue is more and more crucial as regarded to the field of Ambient Intelligence (AmI). Specifically, the exact concept of technologies embedded in the patients' surrounding environment implies a strong impact on their everyday life, which can be perceived as a limitation to autonomy and privacy, and therefore refused or even openly opposed by the final users. The present contribution tackles this issue directly, highlighting: (1) a theoretical framework to include patient engagement in the design of AmI technologies; (2) assessment measures for patient engagement while developing and testing the effectiveness of AmI prototypes for healthcare. Finally (3) this contribution provides an overview of the main issues emerging while implementing AmI technologies and suggests specific design solutions to address them.