A randomised controlled trial comparing internet-delivered Cognitive Behavioural Therapy (iCBT), internet-delivered Mindfulness-Enhanced Cognitive Behavioural Therapy, internet-delivered Mindfulness Skills Training versus usual care for adults with depression and/or anxiety.

INTERVENTION: Participants will complete one of the three interventions described below. The internet‐delivered Mindfulness‐Enhanced Cognitive Behavioural Therapy Program comprises 6 lessons completed over 14 weeks. It includes all treatment components typically seen in face‐to‐face cognitive behavioural therapy (CBT), as well as a number of formal and informal mindfulness exercises (including guided mindfulness meditations (provided on a CD) and written instruction for using mindfulness in daily life). One lesson will be completed every 7‐14 days (it will become available after the preceding lesson has been completed, with a minimum of 5 days between lessons). Each lesson will take approximately 30‐40 minutes to complete. Participants will have access to summaries of each lesson, homework exercises, extra resources, for each lesson. Clinician guidance will be provided in the form of email and/or phone contact from the clinician (registered clinical psychologist) after completion of the first two lessons, then as required. The participant is also able to email or phone the clinician at any point during the trial as required. The participant completes a measure of psychological distress before each lesson and if their scores increase by one or more standard deviations the clinician is automatically alerted and initiates contact with the participant by phone or email. The internet‐delivered Cognitive Behavioural Therapy Program comprises 6 lessons completed over 14 weeks. It includes all treatment components typically seen in face‐to‐face cognitive behavioural therapy (CBT). One lesson will be completed every 7‐14 days (it will become available after the preceding lesson has been completed, with a minimum of 5 days between lessons). Each lesson will take approximately 30‐40 minutes to complete. Participants will have access to summaries of each lesson, homework exercises, extra resources, for each lesson. Clinician guidance will be provided in the form of email and/or phone contact from the clinician (registered clinical psychologist) after completion of the first two lessons, then as required. The participant is also able to email or phone the clinician at any point during the trial as required. The participant completes a measure of psychological distress before each lesson and if their scores increase by one or more standard deviations the clinician is automatically alerted and initiates contact with the participant by phone or email. The internet‐delivered Mindfulness Skills Training Program comprises 6 lessons completed over 14 weeks. It includes a number of formal and informal mindfulness exercises (including guided mindfulness meditations (provided on a CD) and written instruction for using mindfulness in daily life). One lesson will be completed every 7‐14 days (it will become available after the preceding lesson has been completed, with a minimum of 5 days between lessons). Each lesson will take approximately 30‐40 minutes to complete. Participants will have access to summaries of each lesson, homework exercises, and mindfulness recordings. Clinician guidance will be provided in the form of email and/or phone contact from the clinician (registered clinical psychologist) after completion of the first two lessons, then as required. The participant is also able to email or phone the clinician at any point during the trial as required. The participant completes a measure of psychological distress before each lesson and if their scores increase by one or more standard deviations the clinician is automatically alerted and initiates contact with the participant by phone or email. INCLUSION CRITERIA: * Self‐identified as suffering from depression and/or anxiety. * Australian resident status * At least 18 years of age * Access to a computer, printer, and the internet Strategies used to improved adherence to intervention protocols and procedures for monitoring adherence include: automated email reminders, monitoring the downloading of homework, collection of data on how long participants spent reading lessons and practicing skills. CONDITION: Anxiety Disorder not Otherwise Specified Generalised Anxiety Disorder Major Depressive Disorder Obsessive Compulsive Disorder Panic Disorder with or without Agoraphobia Social Anxiety Disorder PRIMARY OUTCOME: Changes in anxiety symptoms according to mean scores on the Generalised Anxiety Disorder 7‐item scale (GAD‐7). Changes in depression symptoms (according to mean scores on the Patient Health Questionnaire (PHQ‐9) Changes in well‐being according to mean scores on the Warwick‐Edinburgh Mental Well‐Being Scale (WEMWBS) SECONDARY OUTCOME: Changes in experiential avoidance according to the Brief Experiential Avoidance Questionnaire (BEAQ) Changes in in emotion regulation according to mean scores on the Difficulties with Emotion Regulation Scale (DERS) Changes in in functional impairment and disability according to mean scores on the World Health Organisation Disability Assessment Schedule (WHODAS‐II). Changes in mindfulness according to mean scores on the Five‐Factor Mindfulness Questionnaire (FFMQ) Changes in psychological distress according to mean scores on the Kessler‐10 (K10). Changes in repeptitive thinking frequency according to mean scores on the Repetitive Thinking Questionnaire (RTQ‐10) Changes in severity of social anxiety according to mean scores on the Social Phobia Inventory (SPIN). Changes in the frequency of avoidance and safety behaviours according to the Worry Behaviours Inventory. Changes in the severity of panic disorder symptoms according to mean scores on the Panic Disorder Severity Scale (PDSS). Changes in wellbeing according to scores on the World Health Organisation 5‐item wellbeing scale. Treatment Satisfaction according to the scores on the Treatment Satisfaction Questionnaire. Unwanted/negative side effects of the internet program as defined as the self‐reported number of unwanted problems or events that participant reported occurring due to participation in the program. * Meet criteria for either Major Depressive Disorder (MDD), Generalized Anxiety Disorder (GAD), Social Phobia (SP), Panic Disorder (PD), Agoraphobia (AG), Disorder or Obsessive‐Compulsive Disorder (OCD) according to the Anxiety Disorders Interview Schedule for DSM‐5 * If taking medication, must have been taking the same dose for at least 1 month and not intend to change that dose during the course of the program. * Prepared to provide name, phone number, and address, and to provide the name and phone number of a local general practitioner. * Willing to provide informed consent. * Willing to be randomised to one of the three treatment conditions or usual care.