Eligible work will be a multi-installment science fiction or fantasy story, unified by elements such as plot, characters, setting, and presentation, which has appeared in at least three installments consisting of a total of at least 240,000 words, by the close of the calendar year 2017, at least one installment of which was published in 2017.

Caution: Series which were Finalists in this category in 2016 may not be eligible. Although the Best Series Hugo in 2016 was a one-time convention award, it is quite possible that the Hugo Administrator will rule those Finalists ineligible according to the WSFS rules for the new ongoing Best Series Hugo