Mental toughness is a psychological trait involving confidence, emotional and behavioral control, commitment to goals, persistence under stress, and an intermediate belief to interpret challenges as opportunities for growth, enabling individuals not only to endure adversity but also to function effectively and pursue excellence. It is a measure of an individual’s psychological resilience and confidence under pressure, adversity, uncertainty, and challenge. Mental toughness shares key characteristics with grit and may predict success in sport, education, and professional settings. Near-synonyms of mental toughness include hardiness, determination, strong-willed, and stalwart.

The concept emerged in the context of sports training and sports psychology as one of a set of attributes that allows a person to become a better athlete, cope with difficult training and competitive situations, and emerge without losing confidence.^{[citation needed]} The term has been used by coaches, sport psychologists, sports commentators, and business leaders.

"Mental toughness" is frequently used colloquially to refer to any set of positive mental attributes that helps a person to cope with difficult situations. Coaches and sport commentators freely use the term mental toughness to describe the mental state of athletes who persevere through difficult sport circumstances, such as playing while hurt, to succeed. In support of this, a number of studies have linked mental toughness to sporting success or achievement. However, the phrase is often simply applied as a default explanation for any victory. This imprecise use of the term has drawn criticism.

Scientific research has attempted a formal definition of mental toughness as a psychological construct with clear measurement criteria, which would allow robust analyses and comparisons to be made.

In particular, three research teams produced both a definition and a construct definition for mental toughness: being able to push past failures or blockades by remaining positive and competitive. This involves training the mind to be ready for challenges.

Graham Jones, Sheldon Hanton, and Declan Connaughton of the United States used personal construct psychology in interviews with elite athletes, as well as elite-level coaches and sport psychologists, to arrive at the following definition of mental toughness:

Having the natural or developed psychological edge that enables you to: generally, cope better than your opponents with the many demands (competition, training, lifestyle) that sport places on a performer; specifically, be more consistent and better than your opponents in remaining determined, focused, confident, and in control under pressure.

These same researchers published a second paper which provided four dimensions (categories) for mental toughness attributes: a general dimension of a performer's attitude or mindset (specifically, the performer's focus and self-belief), and three time-specific dimensions: training, competition, and post-competition. These time-specific dimensions contain attributes of mental toughness (such as handling pressure, handling failure, and pushing yourself to your physical limit in training) that pertain to their use at those times.