Health technologies are increasingly used to support diagnosis, treatment, and symptom monitoring. In this context, health technology which is not well accepted can result in people discontinuing or refusing care. Many factors influence a person’s acceptance of technology, for instance one’s trust in the technology or those who provide it. Designers have been trying to account for facilitators and barriers to technology acceptance. However, they are often unsure of how to use the numerous theories of user acceptance in their own practice. This work presents the Technology Acceptance (TAC) toolkit: a novel theory-based design tool. The TAC toolkit was evaluated through workshops conducted with 21 designers of health technologies (including human-computer interaction researchers, engineers, and clinical psychologists). Findings showed that the toolkit effectively bridged theory and design practice, helped design for long-term user acceptance, and facilitated conversations on user acceptance. This work won a Best Paper Award (top 1% of over 3,000 submissions) at the leading international venue for Human-Computer Interaction research. Additionally, the TAC Toolkit has been wildly distributed (over 100 copies worldwide) and used by research groups including NetwellCASALA (Dundalk), Cumulus Neuroscience (Belfast), CACHET (Copenhagen), and Munster Technological University.