Even where institutions have a central research software team, there is still scope for software development work to be undertaken by researchers/developers in individual research groups. Research software communities are a great way to support a "grass roots" base of researchers and developers building software, helping them enhance their skills, network with peers and build new collaborations. In this talk I'll provide my perspective on the benefits of research software communities and look at examples of building a UK-based local, institutional community and a wider regional community. Through these examples, I'll look at challenges faced in starting and sustaining such communities and highlight some of the key benefits they can offer.