Board and Card Game (BCG) sites allow people to connect over the Internet to play virtual versions of games, like Chess or Canasta, that can be played on a physical table. Many of these sites are successful as they have large memberships, are extremely active, and persist for a long time. However, when analysing the BCG site PlayOK, I found that the community did not exhibit behaviours traditionally associated with successful community: there was little verbal communication; most interactions were impersonal and once-only; and the player population was highly transient. The problem is that designers and researchers have a poor understanding of the characteristics of BCG communities, and how those characteristics are affected by factors that are typically seen as important for community such as size and leadership. In this thesis, I improve understanding of BCG site communities through three studies: 1 No research describes community behaviour in BCG sites. I analysed community behaviour in the PlayOK BCG using ‘social accounting’ methods, which generate summary behavioural statistics from log traces. I found that players were motivated by wanting an opponent, without being concerned with the opponent’s identity. 2 The effects of community size on BCG community behaviour are poorly understood. I used social accounting analyses to compare a small site (GameCenter), with the large PlayOK site. I found that the smaller GameCenter exhibits very similar behaviour but is less efficient due to the smaller population. 3 There are no empirical studies of the role of leadership in online game communities through a substantial change in leadership. I used social accounting techniques to analyse GameCenter BCG before and after a substantial change in leadership. I found that sub-communities responded differently according to how they relied on the leadership for their core activities. This research is the first to identify a type of community that is sustained through impersonal, non-verbal interactions. This important because examples exist in BCG sites and may exist as sub-communities in other settings such as online discussion forums, social media sites, and other online games.