The financial success of many Vertigo titles relied not on monthly issue sales, but on the subsequent "trade paperback" editions that reprinted the monthly comics in volumes, which were also sold in general-interest bookshops. Vertigo's success in popularizing this approach led to a wider take-up in the American comics industry of routinely reprinting monthly series in this format. Limited series (ideal for later collection) and original graphic novels made up the majority of the imprint's output, with trade paperback sales accounting for a substantial segment of the imprint's sales.