The number of people aged 65 or older, both within Europe and globally, is projected to increase substantially by 2050, nearly doubling from the 2018 figure of 101 million. At the same time, elderly are looking to stay in their homes as long as possible, which increases the need for a different level of support. Services that are focusing on volunteering and helping others can be of great importance in this regard. The COVID-19 pandemic also showed the vulnerability of elderly who suddenly were recommended not to meet too many people and to avoid stores. As a result, they became dependent on other people, even for tasks that they might have been able to do by themselves. As physical meetings had to be avoided, the importance of digital social engagement platforms has become clearer. However, the use of digital social engagement platforms poses two problems: 1) There are indicators that older people are lagging behind in adopting new technologies, while computer and internet-based services have become prevalent in the modern world and in particular during the COVID-19 pandemic; and 2) The acquisition and especially retention of volunteers is not without challenges. 

In this dissertation, we have addressed both problems from a computer science point of view. First, we investigated what is required to make digital social engagement platforms that are focusing on requesting and offering help for everyday tasks more accessible to elderly. For this, we used a comprehensive view at the topic covering both social as well as technical and design issues, but dealing with them from the perspective of computer science. To address the first problem, we first took an in depth look at technology adoption factors focusing on older users. Next, we looked at current usability guidelines focusing on designing technologies for elderly and investigated their relevance for modern technology. To deal with the second problem, we searched and explored techniques that are known or could be used for motivating and engaging users. More specifically, gamification, persuasive strategies, and nudging were considered. 

After having studied the two problems from a general point of view, we returned to our concrete use case, social engagement platforms. The COVID-19 pandemic brought several social engagement platforms to the spotlight, including existing ones as well as new ones. An extensive evaluation of several of these platforms has been conducted to examine how well they address the two problems mentioned. This evaluation was performed by means of hands-on evaluations, interviews with representatives from five platforms, and user surveys conducted on three of the platforms (resulting in more than 800 responses, from users in Finland and Belgium). 

Based on all the results, we compiled a list of recommendations on how existing social engagement platforms might become more accessible to elderly, and could stimulate the long-term engagement of their users. A pilot study with elderly was performed to evaluate some of our key recommendations. Finally, we also discussed and proposed a new approach on how gamification could be utilized in this context for bridging inter-generational divides. The concepts are illustrated by the means of an early proof of concept.

The core contributions of this dissertation are: 
- An up-to-date overview  of the research field on the adoption and use of digital technology by elderly. 
- An up-to-date list of usability design guidelines for elderly users, evaluated with experts. 
- An overview of gamification, persuasive technology, and nudging, and their effectiveness as reported in the literature.  
- A thorough evaluation of existing social engagement platforms.
- A list of recommendations on how social engagement platforms might become more accessible to elderly as well as on how they could better stimulate the long-term engagement of their users, together with a first evaluation. 
- A new approach for using gamification in these types of platforms to stimulate long-term engagement and with the potential to bridge inter-generational divides.