Toei Animation Europe announced that a second season of Bishoujo Senshi Sailor Moon: Crystal (Pretty Guardian Sailor Moon: Crystal) is planned to start this Summer after the season's finale on July 18. It is currently unknown how many episodes the second season will have.

Bishoujo Senshi Sailor Moon is a classic bishoujo manga from the '90s and was adapted into several anime series. The new series, based on the manga, started streaming on Nico Live in Summer 2014 bi-weekly and is currently airing on TV as of April 1.

Source: Toei Animation Europe official site


Update June 10
The original announcement by Toei Europe caused a misunderstanding due to Toei Europe referring to Crystal's Black Moon arc as second season. There is currently no confirmation of a second season.

Source: Sailor Moon official site