John Rupert Firth (1890-1960) was one of the most influential linguists in Great Britain in the 1940s and 1950s. Around him developed a loosely framed school of thought which is usually referred to as the London School of linguistics. Many aspects of Firth's approach to the study of language are still of relevance today and would resonate well with contemporary functional, pragmatic and interactional approaches that are interested in analysing meanings and the systematicities underlying the use of language. The aim of this article is to give a balanced view of Firth's central ideas, examining Firth's theory from a general perspective; discussing Firth's approach in terms of the levels of analysis and modes of meaning that he distinguished; addressing the main underpinnings of Firth's approach to the study of linguistic phenomena at any level of analysis: as multiple structures (or patternings) and multiple sets of alternative options; dealing with some other central ideas in Firth's theory: restricted languages, speech fellowships, collocations and colligations; and finally, assessing Firth's contribution to linguistics in the light of the impact it has had on contemporary linguistics. As a postscript, it briefly considers Firth's theory from the perspective of pragmatics.