Mindfulness-based cognitive therapy (MBCT) and mindfulness-based stress reduction (MBSR) are particularly effective treatment approaches in terms of alleviating depressive symptoms and preventing relapse once remission has been achieved. Although engaging in mindfulness practice is an essential element of both treatments; it is unclear whether informal or formal practices differentially impact on symptom alleviation. The current study utilizes a correlational design to examine data provided by thirty-two previously depressed, remitted outpatients who received either MBCT or MBSR treatment. Outpatients in the MBCT group received treatment as part of a previously published randomized efficacy trial (Segal et al. in Arch Gen Psychiatry 67:1256–1264, 2010), while those in the MBSR group received treatment as part of a separate, unpublished randomized clinical trial. Throughout treatment, clients reported on their use of formal and informal mindfulness practices. Results indicate that engaging in formal (but not informal) mindfulness practice was associated with decreased rumination, which was associated with symptom alleviation.