With Diana Gabaldon's Written in My Own Heart's Blood securing the top spot on a number of sales lists, it's clear fans are not tired of her Outlander world. Next year, J.D. Robb will release her fortieth full-length In Death series book, while Nalini Singh, Kresley Cole, J.R. Ward, and other authors show no signs of stopping their respective series. That's a lot of books in series for fans to read, and definitely requires commitment.
What is the longest series you've kept up with?