Background: Multiple Sclerosis (MS) is a chronic condition of the central nervous system; around 1 in 600 people in the United Kingdom have MS. Many people with MS (70%) have cognitive difficulties, which they experience as distressing and disabling, and there is currently a lack of treatment options to improve these difficulties. SMART (Strengthening Mental Abilities with Relational Training) - a theory-based online cognitive training programme, which has been shown to improve general cognitive abilities - has not been tested with people who have MS.

Aims: To conduct a feasibility study to inform development of a definitive trial of SMART for improving cognitive functioning in people with MS. The investigators will assess: 1. Acceptability to participants of the intervention, delivery format, inclusion/exclusion criteria, baseline and outcome measures, randomisation protocol, and study procedures 2. The framework for a cost-effectiveness analysis alongside a definitive trial 3. Participant recruitment and retention rates 4. Sample-size needed for fully powered trial 5. Signal of efficacy Plan: To address Aims 1-5, the investigators will recruit 60 adults with MS who are experiencing cognitive difficulties, identified from MS clinics. Participants will complete baseline assessments of their cognitive abilities and answer questionnaires about their cognitive difficulties, personal priorities, mood, fatigue, self-efficacy, quality of life, and healthcare services used. Assessments will be administered by a researcher, face-to-face or remotely. Participants will be randomly allocated to one of three arms (20 per group): Group 1: Receives SMART intervention online - plus usual care (MS Nurse support). SMART intervention involves completing a series of logic problems, which are designed to train skills that scaffold complex cognition. Group 2: Receives usual care alone. Group 3: Receives a 'control' intervention online - plus usual care. Baseline measures will be re-administered at three- and six-months post-randomisation. Researchers and patient-partners (people with personal experience of MS, who will act as co-researchers) will also interview 30 participants about their experience of the study and treatment. All qualitative data will be transcribed and thematically analysed in terms of a priori feasibility aims. Quantitative data will enable sample-size calculation for a definitive study and determine signal of efficacy.