This paper examines the ‘what’, ‘why’ and ‘how’ of employee well-being. Beginning with the ‘what’ of well-being, the construct of mental health was explored with the aim of building a model of employee well-being. It was proposed that employee well-being consists of three core components: (1) subjective well-being; (2) workplace well-being and (3) psychological well-being. Following this, the ‘why’ of employee well-being was investigated; that is, why employee well-being should be an important matter for organisations. It was argued that employee well-being is an important precursor to organisational well-being, as indicated by its links to employee turnover and performance. The next section was concerned with the ‘how’ of employee well-being; that is, how well-being can be reliably enhanced. Drawing on two models of strengths and a practice model of psychological assessment, it was asserted that strength-based development can reliably enhance employee well-being. A solid framework for understanding and measuring employee well-being is offered in the hope that it will foster a more integrated approach to assessing and optimising employee well-being.