What is ACT?

Dr. Russ Harris Explains Acceptance and Commitment Therapy

If you’re a therapist, or client, trying to figure out if ACT is the right framework for you, hearing from Dr. Russ Harris is a good place to start.  Author of best-selling book The Happiness Trap, as well many other ACT-related books for both clients and therapists, Russ is arguably the world-leading trainer on Acceptance and Commitment Therapy, and much beloved for his vibrant, down-to-earth teaching style.

In this short video, Russ goes back to basics to answer the question: what is ACT?  He explains how ACT differs from other therapies, especially in its focus on cultivating a fulfilling, values-driven life, rather than just reducing or eliminating symptoms.  

How Does ACT Work?

As Russ explains, the goal of ACT (pronounced as the word “act” rather than a-c-t) is to support clients to accept things that are outside of their personal control, and then commit to taking active steps to solve their problems and change their habits in ways that can improve their day-to-day lives.  This is achieved through a series of strategies that help clients develop what is technically called psychological flexibility. 

ACT aims to empower clients to build their capacity for greater psychological and emotional presence, as well as more openness to experience.  This is so they can cultivate more self-awareness about what is important to them (their values), then take inspired action in the pursuit of what they want.  Acceptance and Commitment Therapy doesn’t ask clients to challenge their anxieties, silence their harsh inner critic, or work through painful memories.  Rather, it invites clients to accept these experiences, and then actively commit to living a meaningful, rewarding life in their continued presence.  

Occasionally, the word “acceptance” can sometimes evoke hesitation in prospective patients, as they worry they might have to resign themselves to suffering, or give up on the possibility of change.  However, as Russ highlights, ACT is a highly active treatment that focuses on opening up to difficult internal experiences, rather than fighting them.  The ACT model also helps clients realize that a great percentage of their suffering is often actually caused by their reactions and resistances to their symptoms.  By cultivating genuine acceptance of their pain, they can paradoxically create a new freedom, and restore energy to focus on what really matters.  This theoretical shift from other cognitive models might seem subtle, but has made ACT one of the fastest-growing evidence-based therapies in the world.

The Theoretical Basis for ACT: Relational Frame Theory 

Relational Frame Theory was developed by ACT founder Professor Steven C. Hayes and his colleagues at the University of Nevada, and provides the rationale for how ACT works.  Through his experiments relating to language and cognition, Hayes discovered that ideas, thoughts and memories can end up carrying the same emotional weight as the original experience they are related to. 

That is to say, thoughts themselves can wind up having a disproportionate impact on an individual’s psychological and emotional life.  These discoveries paved the way for ACT’s framework of pragmatic interventions, which focus on returning thoughts and memories to their rightful place when they have become too literal, fused or influential in the client’s inner life. 

How Does ACT Differ From CBT?

ACT is often described as a “third wave” cognitive behavioural therapy, which leads to the question: how is ACT different from CBT?  Traditional CBT works, in large part, by identifying and challenging tightly held thoughts — helping clients recognize cognitive errors and replace unhelpful thinking with more accurate or balanced alternatives.  ACT therapists take a different approach. Rather than challenging the content of thoughts directly, they help the client to create a different relationship to their thoughts.

From an ACT perspective, a thought doesn’t need to be true or false, helpful or unhelpful — the client just needs a way to put the thought in a place where it is no longer interfering so much in their life.  This distinction is significant, particularly for therapists and clients who find the more directive thought-challenging strategies of CBT invalidating or ineffective in creating sustainable change.

In practice, many clinicians find the two approaches complement each other well. ACT’s emphasis on values and committed action integrates naturally with the more behavioural aspects of CBT, including behavioural activation and graded exposure.

What Presenting Problems Is ACT Used For?

One of ACT’s strengths is its trans-diagnostic applicability. Because it targets psychological inflexibility as an underlying process, rather than disorder-specific symptoms, it can be adapted well across a wide range of clinical presentations.  There is strong evidence supporting its effective use in treating depression, anxiety, trauma, chronic pain, health anxiety, and substance misuse (Levin, Krafft, and Twohig, 2024).  As demonstrated by Russ’ wide body of published works, ACT can also be used to address a range of non-diagnostic problems that individuals struggle with in their everyday lives, including grief and loss, people-pleasing and perfectionism, weight loss, stress and burnout.  

ACT has also been found to be especially useful in the treatment of young people (López-Pinar, Lara-Merín, and Macías, 2025).  Adolescents often struggle to articulate or challenge their thinking in the way traditional CBT requires, but the experiential and values-based nature of ACT can be easier to engage with, particularly when delivered through metaphor, creative exercises, or movement.

Is ACT Suitable for Neurodiverse Patients?

ACT is especially suitable for adaptation as a neurodiversity-affirming model.  The emphasis on values-clarification and acceptance of internal experience, rather than behaviour normalisation, makes ACT an ideal therapy for people living with neurodiversity.  In the context of increasing calls for the treatment of conditions like autism to be conducted from a more neuro-affirming lens, ACT provides a pragmatic framework for clinicians looking to ensure that their practice aligns with this ideology.

Emerging literature also supports the use of ACT in the treatment of people with intellectual impairments and autism (Byrne & O’Mahony, 2020), the parents of autistic children (Maughan, Lunsky, and Weiss, 2023), and people with ADHD (Munawar et al. 2021).  Many of the functional difficulties associated with ADHD also map directly onto the capacity for psychological flexibility, offering a strong rationale for the use of ACT with this population. 

Overall, ACT tends to resonate strongly with clients who feel stuck despite understanding their patterns, who have tried to “think positively” without lasting effect, or who are exhausted by the effort of managing their inner world.  For therapists, ACT provides something unique - the confidence and grounding of a suite of specific techniques, but within a philosophically flexible model that can be adapted to suit a wide range of clients from all walks of life.