1.1 Definition of mental health and wellbeing
The World Health Organization (WHO) defines ‘mental health’ as: 
“…a state of well-being in which every individual realizes his or her own potential, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to her or his community.”
The importance of mental health in determining the holistic health of an individual is clearly stated in the WHO’s constitution: 
“Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.”
By contrast, ‘mental health problems’ have been defined as conditions affecting an individual’s mood, thinking and behaviour to a degree that impacts significantly on their ability to function within different areas of life. 
These definitions stress the importance of treating physical and mental health equally to achieve ‘parity of esteem’. To succeed in this requires health professionals to reconsider how they treat individuals, addressing the needs of the whole person rather than separately treating their physical and mental health. This is particularly important when considering the relationship between physical and mental ill health, as illustrated in Figure 1.
Figure 1 – The percentage of people affected by depression with various illnesses (from NHS England’s A Call to Action: Achieving Parity of Esteem; Transformative Ideas for Commissioners) 
 WHO (2014) Mental health: a state of wellbeing. Available at: http://www.who.int/features/factfiles/mental_health/en/ (accessed 30/09/2015).
 Law et al. How big an issue is children and young people’s mental health? Young Minds doc from Steve
 NHS England (2013 – check this) A Call to Action: Achieving Parity of Esteem; Transformative Ideas for Commissioners.