The principles and practices of Yoga (or Yoga Psychology) were developed in ancient times, offering a wholistic, integrative system of mental health that is just as relevant today
The system of Yoga developed and taught by Patanjali (the great Indian sage from over 2000 years ago) is defined as the development and refinement of the mind - what the mind is, how it works, known limitations and dysfunctional tendencies, what we can do to improve it's functioning and what it might be capable of - with understanding and specific practices. This system of Yoga described by Patanjali includes a wholistic understanding of the mind in the context of a physical, breathing, social being, with implications for behaviour change, personal transformation and living a flourishing life. Yoga itself is a well-developed system of psychology.
'Yoga' in the modern world though is no longer a term primarily associated with this ancient system presented in Patanjali's Yoga Sutra's. Modern yoga is a much broader concept which includes a growing number of styles and approaches, often associated predominately with physical postures and group classes (gentle or intense, calming or energising, whatever you like!), taught by people with a diverse range of education, training and experience.
Yoga in the tradition of Patanjali offers teachings and practices to develop a personal experience of the subtle mind-body-breath connection. In Yoga, this connection is more important than physical strength or flexibility. It is instead the qualities of the mind which are central to the teachings and practices of Yoga.
Yoga (or Yoga Psychology) offers practices to enhance mental health and alleviate the symptoms of psychological ill-ease or mental illness,using mind-body-lifestyle interventions to cultivate a healthy, productive, flourishing life.