BACKGROUND: Increasing age is associated with a natural decline in cognitive function and is the greatest risk factor for dementia. Cognitive decline and dementia are significant threats to independence and quality of life in older adults. Therefore, identifying interventions that help to maintain cognitive function in older adults or that reduce the risk of dementia is a research priority. Cognitive training uses repeated practice on standardised exercises targeting one or more cognitive domains and may be intended to improve or maintain optimal cognitive function. This review examines the effects of computerised cognitive training interventions lasting at least 12 weeks on the cognitive function of healthy adults aged 65 or older and has formed part of a wider project about modifying lifestyle to maintain cognitive function. We chose a minimum 12 weeks duration as a trade-off between adequate exposure to a sustainable intervention and feasibility in a trial setting. OBJECTIVES: To evaluate the effects of computerised cognitive training interventions lasting at least 12 weeks on cognitive function in cognitively healthy people in late life. SEARCH METHODS: We searched to 31 March 2018 in ALOIS (www.medicine.ox.ac.uk/alois), and we performed additional searches of MEDLINE, Embase, PsycINFO, CINAHL, ClinicalTrials.gov, and the WHO Portal/ICTRP (www.apps.who.int/trialsearch), to ensure that the search was as comprehensive and as up-to-date as possible to identify published, unpublished, and ongoing trials. SELECTION CRITERIA: We included randomised controlled trials (RCTs) and quasi-RCTs, published or unpublished, reported in any language. Participants were cognitively healthy people, and at least 80% of the study population had to be aged 65 or older. Experimental interventions adhered to the following criteria: intervention was any form of interactive computerised cognitive intervention - including computer exercises, computer games, mobile devices, gaming console, and virtual reality - that involved repeated practice on standardised exercises of specified cognitive domain(s) for the purpose of enhancing cognitive function; the duration of the intervention was at least 12 weeks; cognitive outcomes were measured; and cognitive training interventions were compared with active or inactive control interventions. DATA COLLECTION AND ANALYSIS: We performed preliminary screening of search results using a 'crowdsourcing' method to identify RCTs. At least two review authors working independently screened the remaining citations against inclusion criteria. At least two review authors also independently extracted data and assessed the risk of bias of included RCTs. Where appropriate, we synthesised data in random-effects meta-analyses, comparing computerised cognitive training (CCT) separately with active and inactive controls. We expressed treatment effects as standardised mean differences (SMDs) with 95% confidence intervals (CIs). We used GRADE methods to describe the overall quality of the evidence for each outcome. MAIN RESULTS: We identified eight RCTs with a total of 1183 participants. The duration of the interventions ranged from 12 to 26 weeks; in five trials, the duration of intervention was 12 or 13 weeks. The included studies had moderate risk of bias, and the overall quality of evidence was low or very low for all outcomes. We compared CCT first against active control interventions, such as watching educational videos. Negative SMDs favour CCT over control. Trial results suggest slight improvement in global cognitive function at the end of the intervention period (12 weeks) (standardised mean difference (SMD) -0.31, 95% confidence interval (CI) -0.57 to -0.05; 232 participants; 2 studies; low-quality evidence). One of these trials also assessed global cognitive function 12 months after the end of the intervention; this trial provided no clear evidence of a persistent effect (SMD -0.21, 95% CI -0.66 to 0.24; 77 participants; 1 study; low-quality evidence). CCT may result in little or no difference at the end of the intervention period in episodic memory (12 to 17 weeks) (SMD 0.06, 95% CI -0.14 to 0.26; 439 participants; 4 studies; low-quality evidence) or working memory (12 to 16 weeks) (SMD -0.17, 95% CI -0.36 to 0.02; 392 participants; 3 studies; low-quality evidence). Because of the very low quality of the evidence, we are very uncertain about the effects of CCT on speed of processing and executive function. We also compared CCT to inactive control (no interventions). We found no data on our primary outcome of global cognitive function. At the end of the intervention, CCT may lead to slight improvement in episodic memory (6 months) (mean difference (MD) in Rivermead Behavioural Memory Test (RBMT) -0.90 points, 95% confidence interval (CI) -1.73 to -0.07; 150 participants; 1 study; low-quality evidence) but can have little or no effect on executive function (12 weeks to 6 months) (SMD -0.08, 95% CI -0.31 to 0.15; 292 participants; 2 studies; low-quality evidence), working memory (16 weeks) (MD -0.08, 95% CI -0.43 to 0.27; 60 participants; 1 study; low-quality evidence), or verbal fluency (6 months) (MD -0.11, 95% CI -1.58 to 1.36; 150 participants; 1 study; low-quality evidence). We could not determine any effects on speed of processing because the evidence was of very low quality. We found no evidence on quality of life, activities of daily living, or adverse effects in either comparison. AUTHORS' CONCLUSIONS: We found low-quality evidence suggesting that immediately after completion of the intervention, small benefits of CCT may be seen for global cognitive function when compared with active controls, and for episodic memory when compared with an inactive control. These benefits are of uncertain clinical importance. We found no evidence that the effect on global cognitive function persisted 12 months later. Our confidence in the results was low, reflecting the overall quality of the evidence. In five of the eight trials, the duration of the intervention was just three months. The possibility that more extensive training could yield larger benefit remains to be more fully explored. We found substantial literature on cognitive training, and collating all available scientific information posed problems. Duration of treatment may not be the best way to categorise interventions for inclusion. As the primary interest of older people and of guideline writers and policymakers involves sustained cognitive benefit, an alternative would be to categorise by length of follow-up after selecting studies that assess longer-term effects.