People will MS and low mood will be recruited from a neurology outpatient clinic. They will be randomized to either receive treatment as usual, or an ACT self-help book with 8 supportive telephone calls from a trainee clinical psychologist. Measures of anxiety, depression, quality of life and physical health will be administered at baseline, post-intervention and six month follow up. A sub sample of 10 participants will be interviewed to find out their view on taking part in the study.