The ''League of Legends'' Challenger Series (CS) were two professional '' League of Legends'' leagues, one in Europe (EU CS) and one in North America (NA CS), that were the second highest level of professional ''League of Legends'' in those regions. The two highest-placing teams from the Challenger Series played in the ''League of Legends'' Promotion Tournament against the two lowest-placing ''League of Legends'' Championship Series (LCS) teams, the winners of which were promoted to the Championship Series in each region, whereas the losers were relegated to the Challenger Series. The league was announced in December 2013 and began play for the Spring 2014 season. Both the NA and EU CS were discontinued in 2018 in preparation for league franchising.

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{{League of Legends League of Legends competitions Sports leagues established in 2014 Sports leagues disestablished in 2018