It came from clinical practice.

It all began around 1980, when William R. Miller, a psychologist from Albuquerque, New Mexico, US was visiting Bergen, Norway on sabattical.  He held a series of seminars with a group of Norwegian psychologists who peppered him with questions about why he was doing what he was doing with clients who were struggling with alcohol dependence. The outcome was a paper entitled "Motivational Interviewing" that was submitted to Dr Ray Hodgson, the editor of a journal called "Behavioural Psychotherapy".

Miller went back to Albuquerque and what unfolded was the merging of clinical practice with research. He conducted a range of studies with colleagues in the Department of Psychology, University of New Mexico, on how poeple respond to an empathic style when talking about change and receiving feedback.

In 1989 Miller met Stephen Rollnick, who had taken up motivational interviewing in the UK. They met in Sydney, Australia, and wrote the first edition of the standard text, Motivational Interviewing.  Initially this was focussed largely on the addictions field.

Over the following twenty years, what emerged was a group of like minded colleagues, who formed the Motivational Interviewing Network of Trainers (MINT), a system for training trainers, broader application in health care, social care and criminal justice, and an exponential rise in the number of trials examining the efficacy of motivational interviewing.