This paper explores the role of language in the construction of Welsh identities in London. It begins by mapping out some key theoretical connections between language, geography and identity, and argues that a reading of diaspora theory might be helpful in conceptualizing Welsh identities in the British capital. In particular, diaspora theory stresses that identities are made up of multiple social axes that need to be seen relationally. Diasporic identities make connections with more than one place challenging the notion of culture and language as delimited by the boundaries of particular national spaces. For many Welsh people in London, language is an important part of their attempts to meet others who share a common identity. London-Welsh societies facilitate this need, defining language in different ways, and interweaving the linguistic with other social axes to form powerful senses of belonging. Whilst London is a key migration destination, it is also a space of Welsh identities that draw centrally upon language, but make different geographical connections with Wales. The paper concludes by arguing that a diasporic reading of such processes allows a wider and more progressive understanding of the Welsh language, and highlights the importance of geography in doing so.