Like physical health, 'mental health' fluctuates and exists on a continuum. Because each individual has their own experience with emotional wellbeing, mental health conditions and mental illnesses, mental health varies widely from person to person.

'Mental illness', like any medical problem, is a diagnosed condition that affects one's emotions, behaviours, or relationships and could cause challenges to social functioning. With proper care, these symptoms can be mitigated and even treated, giving those with such illness the ability to function well in their daily lives.

On the flip side of mental illness, 'wellbeing' can be defined by the emotional, social and psychological ability of a person to be happy, attentive, and manage emotions while lacking behavioural problems that affect their lives. Anxiety, depression or violence may be signs of a lack of well-being.

There are more people at work with mental health conditions than ever before. In recent years, the proportion of workers that can expect to experience some form of mental health problem during their working lives has increased markedly. Mental health problems are a leading cause of illness and disability. Mental ill-health can have a significant impact in the workplace, whether a result of acute and severe ill-health or milder ill-health.

Untreated mental health, especially if combined with poorer physical health can lead to absenteeism, decreased work performance, negative attitudes and behaviours, and poor working relationships with colleagues and clients. There are also several important intersections to this issue. For example, women in full-time employment are twice as likely to have a common mental health problem compared to full-time employed men.

The "invisibility" of poor mental health and illness makes it difficult for people to identify it in themselves and others. Because mental health tends to be a sensitive and intimate topic, people affected are unlikely to feel confident to be forthcoming about their situation. Such discomfort in communication can strain the employee-manager relationship. Less than half of employees say they feel able to speak openly about stress with their line manager. One in four people even consider resigning due to stress. However, despite a push for transparency, in 15% of cases where the employee disclosed a mental health issue to a line manager, the employee became subject to disciplinary procedures, dismissal or demotion.

As such, well-being and mental health might also be considered through the lens of workplace diversity, and through organisational culture.

The Mental Health Foundation estimates that better mental health support in the workplace would save UK businesses up to £8 billion per year. Others, including the Centre for Mental Health, estimate costs to be several times higher. Additionally, Deloitte's analysis of investments made in improving mental health shows a consistently positive return on investment. There is a clear business case for organisations to equip themselves with a holistic approach to mental health in the workplace. Well-managed businesses are likely to understand the importance of promoting awareness and employing tools and processes to identify, address and prevent poor mental health caused or worsened by work.