The book explores written language across communication device types. Challenging the current norm of a "device-neutral" approach, it argues that the physical device (smartphone, computer) plays a complex role in language use, similar to other contextual factors. A three-part computational sociolinguistic study is used to investigate the variation of nineteen microlinguistic features (message length, capitalisation, acronyms, emoji, etc.) across device types, using two corpora of Twitter/X and Discord messages. The work develops an innovative approach for investigating the influence of technology on written language, highlighting the value of affordances over technological determinism.