Healthcare services that consistently meet the needs of service users have to be designed. The growing demand for better quality of care, together with an increasing awareness of limited resources, are bringing attention to the need for design in healthcare. In mental health, considered the largest cause of disability in the UK, the need is great. Existing services often fail to meet demands and do not consistently deliver good quality care for all service users. The design of better delivery systems has the potential to improve service user experience and care outcome. But, where do we start? This paper reports the first stage of an ongoing research to co-design a language for designing mental health services. This stage of the research identified, through focus groups and interviews with service users and clinicians, the key components of a mental health service. This paper argues that an appropriate concept of a mental health delivery service as a system, the identification of its key components and an understanding of the association between these components form an essential first step in designing such a system.