Telehealth can provide benefits to heart failure and chronic obstructive pulmonary disease (COPD) patients, however large scale deployment is still yet to be achieved. This thesis aimed to investigate what predicts optimal telehealth usage among heart failure and COPD patients. A systematic review found that 32% of patients who are offered telehealth failed to accept it and 20% of patients who did accept later abandoned telehealth. The review also recommended the need for further qualitative work to explore the facilitators and barriers to telehealth in detail. Study 1 explored patients' beliefs and perceptions regarding their ongoing use of home telehealth. Patients described several facilitators of telehealth use relating to: peace of mind, improved self-management behaviour, and better access to healthcare. Conversely, patients also reported how technical problems could become an issue and how they valued face-to-face contact with healthcare professionals. Study 2 consisted of a 'think aloud' study, which assessed the acceptability and face validity of a telehealth acceptance questionnaire, which was developed through the findings obtained from the systematic review and Study 1. The questionnaire was established to have face validity and was found to be acceptable to patients. Study 3 involved a survey study that assessed the reliability and predictive validity of the telehealth acceptance questionnaire. The Self-Report Behavioural Automaticity Index was found to be predictive of telehealth usage compliance, thus suggesting that patients who report their usage of telehealth as being an automatically activated habitual behaviour are more likely to be optimal telehealth users. This work has now led to the development of a valid and reliable tool, which can be used to predict optimal telehealth usage among heart failure and COPD patients who are currently using telehealth.