This review of literature investigates existing user research relating to the UK���s Gallery, Library, Archive and Museum (GLAM) digital collections. Over the last 30 years, the number of online collections, and the number of online visitors using those collections, has increased significantly. Although the use of collections has been on the rise, whether it is meaningful in terms of audience engagement, understanding and appreciation is still questionable, particularly in relation to accurate user behavioural data. A proper understanding of who and how visitors use digital collections is critical for the success of the UK���s galleries, libraries, archives and museums in the information age. This review looks at available work from 2015 to 2021 to compare ways in which users have been categorised, their behaviours and identify areas where further discussion is required. Within the date range; 2015-2021, there is limited material on what characterise user categories leading Rees and Vitale (2020) to state: ���Actual profiles of potential audiences are thin on the ground��� (2020, p. 9). While a range of work on digital audiences exist, in-depth empirical research does appear to have slowed since 2015. There has been a focus within the GLAM sector on quantitative reporting which lacks detail and nuance in terms of audience behaviours. This leads to a lack of richer and deeper understanding of digital users. Analysis of the collection of relevant research identified as having a UK digital collection focus resulted in a total of 87 separate user categories. Audience types were grouped together and described in various levels of detail. There are four key approaches to categorising users within the published and unpublished literature: groupings based on motivation or information seeking behaviour; level of expertise or role e.g. scholarly researcher, professional, engaged amateur and non-expert/general public; mode of interaction; web analytics. A number of studies cited in this review have produced segmentation profiles based on cultural values, independent of specific cultural heritage organisations, collections, systems and situations, which goes some way to provide a shared approach to understanding audiences. These models are not dedicated to digital collections, instead looking at a broad spectrum of cultural heritage and arts activities. A process for applying standardised categories across organisations using motivation as a driver in combination with user dimensions; role, level of expertise, and mode of interaction could be used to create more standardised and consistent user categories across the sector. User Behaviours The available research suggests that that user behaviours are complex. The same individual user could visit a digital collection on multiple occasions but with different objectives and goals. The motivation and mode of interaction segmentation approaches highlight that users can play multiple roles in relation to a digital collection. Users can often switch modes between broad, topic-based searches to known item searches and back again, sometimes in the same session. User motivations broadly range between: casual use, where a user is browsing for pleasure or inspiration rather than searching or researching for specific information. The research suggests that the casual user makes up a large proportion of digital collection users. personal interest, users search for specific information for personal interest. Personal Interest users tend to arrive on the digital collection through looking for terms on search engines; scholarly and professional research, users who are highly motivated and are looking for specific information for research purposes. The research identifies a series of behaviours which can be broadly categorised: Understand ��� users want an overview of the collections or galleries; Explore/Cruising/ Aesthetic - users who are looking for inspiration; Curiosity ��� Enquiry-led users are likely to check a fact or look to answer a specific question. Develop/Digging - share the explorers desire for inspiration but have a stronger sense of focus as their needs are directed to specific topics; Research/Intellectual - users who are very focused and require detailed information on a specific topic or object; Sharing/Social - focussed on object sharing via social media. Non-users The literature suggests that it is difficult to identify categories of ���non-users��� of digital collections due to non-users typically being underrepresented in audience research. It has also been suggested digital collection non-users appear to reproduce similar participation hierarchies and inequalities that already exist in physical cultural heritage settings. COVID-19 audience segmentation A series of audience segmentation approaches have also been devised in response to the impact of COVID-19 on the cultural heritage sector. This segmentation considers the shift in audience needs highlighting the emotional and social needs created by pandemic lock-downs. Leading researchers to suggest that audience behaviour will be different in after the pandemic���, particularly in relation to greater digital engagement. Moving towards Impact and Value Wider literature on digital cultural heritage and audiences suggests a shift away from user behaviour towards impact and value of digital collections and projects. For example; Europeana���s work on impact studies and the role digitised collections can play in providing benefit for social good and economic value. There has also been a growth in bespoke digital resources and projects as standalone endeavours. Crowdsourcing, in particular, has been increasingly explored. Although research suggests that only a small number of ���super users��� (very engaged enthusiasts) make up the large percentage of users and contributors.