Many structural features of the early modern economy governed the working practices of the book trade. Diversity and interconnectedness marked the broader economic structure of publication and bookselling, of capitalization, productive capacity, of supplies of paper and other materials, of demand, of distribution and of trade regulation. The structure of the British book trades changed rapidly from about 1550 to 1650. The balance between different traders and craftsmen shifted as wholesale businesses with onward-selling networks expanded in the late sixteenth century and even more markedly during the seventeenth century. For the majority of metropolitan booksellers, the sales of open market publications became the basis for survival. Cambridge and Oxford were amongst the most prominent, but York, Norwich, Exeter and Bristol, as well as Ipswich, Newcastle and several other towns are identified as established book-trading centres by the beginning of the seventeenth century.