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routine care settings, where patients are not typically followed up after receiving a completed course of treatment. K E Y W O R D S anxiety, depression, iCBT, relapse, remission 1 | I N T R O D U C T I O N Depression and anxiety are leading causes of disability worldwide (World Health Statistics, 2017). The high rates of relapse and recur- rence that characterize these mental health disorders are key factors that contribute to their burden. Between 39% to 56% of individuals who have recovered from their first episode will have one or more further episodes in their lifetime, and the risk of recurrence increases incrementally as a function of the number of episodes previously experienced (Bruce et al., 2005; Burcusa & Iacono, 2007; Vervliet et al., 2013). Given how common and consequential relapses can be, the importance of establishing the durability of treatment effects for anxiety and depression, and identifying factors that confer risk for relapse is readily apparent. Individuals who complete cognitive behavioural therapy (CBT), the leading evidence-based psychological treatment for depression and anxiety, tend to have lower rates of relapse compared to those who discontinue pharmacological treatment (Cuijpers et al., 2013; Hollon et al., 2006; Vittengl et al., 2007). Despite this, considerable risk of relapse also persists after CBT. For instance, recent meta- analyses indicate that relapse rates range from 18.5% to 46.5% for depression (Wojnarowski et al., 2019) and from 13% and 42% for anx- iety (Lorimer et al., 2021), when assessed over the course of 2 years following CBT treatment. Research examining factors that predispose risk for relapse following CBT is still relatively sparse. But, the broader literature on the clinical course of depression and anxiety has identi- fied a range of potential predictors. Gender, age, employment status and socio-economic background have all been implicated, but the per- sistence of residual symptoms and a higher number of previous epi- sodes stand out as factors most consistently linked to increased likelihood of relapse in the long-term (Lorimer et al., 2021; Wojnarowski et al., 2019). In recent years, internet-delivered CBT (iCBT) has been recog- nized as a viable alternative to traditional face-face CBT, and it holds particular promise for its capacity to help address longstanding and pervasive issues pertaining to provider shortages and access problems (Mohr et al., 2021). Several studies have demonstrated both the effec- tiveness of iCBT in treating depression and anxiety (e.g., Andrews et al., 2018; Richards et al., 2020; Wright et al., 2019), and its capacity to produce remission rates that are comparable to face-to-face deliv- ered CBT treatments (Andersson et al., 2018; Andrews et al., 2018; Karyotaki et al., 2018). However, very little is known to date about relapse rates following a course of iCBT. While meta-analyses have shown that there is indeed a maintenance of effects for up to 18 months after iCBT treatment (Andersson et al., 2018; Andrews et al., 2018), these have only explored the durability of effects at an aggregated group-level, and as such, they have not provided any information on relapse rates at an individual-level. Two studies have investigated relapse rates after acute-phase treatment for low- intensity interventions, including but not limited to iCBT, in the Improving Access to Psychological Treatments (IAPT) stepped-care model in the United Kingdom. Ali and colleagues found that 53% of cases relapsed within 1 year, with the majority occurring during the first 6 months (Ali et al., 2017). These figures are very similar to the other study that showed relapse rates of up to 65.8% at 24 months (52.8% at 12 months) for low-intensity interventions in the same set- ting (Delgadillo et al., 2018). Another study, by Klein et al. (2018), examined the potential for internet-based cognitive therapy to pre- vent relapse in a population of remitted recurrently depressed individ- uals. They did not find significant differences in relapse rates between the intervention and control groups over 24 months, with relapse rates of 43% and 49% in each group, respectively (Klein et al., 2018). Collectively, these studies have generally observed relapse rates that are higher than those observed in traditional face-to-face delivered CBT (Hollon et al., 2005; Scott et al., 2003). To the best of our knowl- edge, only two studies specific to iCBT for depression have published on relapse rates. Andersson et al. (2013) found relapse rates of 32.3% over the course of 42 months, and Schure et al. (2020) reported rates of 14.2% over the course of 12 months, respectively. However, these rates were derived from small samples (n = 34 and n = 28, respec- tively), and as such, there may be basis for questioning the generaliz- ability of these findings. Andersson et al. (2013) also highlighted that a large proportion of participants (55%) had sought and received Key Practitioner Message • iCBT has durable effects after an acute phase of treat- ment within a routine care setting. • Relapse rates observed after iCBT treatment are compa- rable to findings observed in face-to-face psychotherapy. • Closer follow-up of younger users, those with long-term conditions, and residual symptoms may be warranted • Usage of iCBT continues beyond the acute treatment period, which may facilitate maintenance of effects. • The content and delivery format of iCBT interventions make them a promising solution to maintenance of effects and long-term remission after an acute phase of treatment. 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