The Caledonian granites of Britain are a wide-ranging suite of pretectonic and posttectonic tonalite-granodiorite-granite intrusions which were emplaced in the time interval 650--380 Ma ago. The volume of magmatic products and the frequency of intrusions increased with time as closure of the Iapetus ocean occurred across the Caledonide belt in the British Isles. Early pretectonic and posttectonic intrusions (older than about 410 Ma) are distinguished from a later (post-410 Ma) group using geophysical (gravity, aeromagnetic, and heat production) and geochemical data. The evidence is interpreted in terms of a trend with time from relatively local thermal and crust-dominated melting events to a final widespread melting event at deeper levels. The latter event produced abundant intrusions with characteristics that resemble the calc-alkaline batholiths of modern destructive margins. Finally, we propose that crustal growth during the Caledonian period took place by northward lateral accretion of the European continental foreland and by vertical accretion of continental crust on both margins by underplating and by later intrusive magmatism.