The Adventurer's League (DDAL), the organized play system for Dungeons & Dragons is changing and it's going to affect players in a huge way.
Since the inception of DDAL players were limited in how they could design their characters. They could use the Player's Handbook, as the PHB has always been the core book for players, and one other option. Colloquially, this rule was called PHB+1.
In case you're not familiar with it, the rule would allow you to use the PHB and Xanathar's Guide to Everything, for example, but you couldn't then use spells from the Sword Coast Adventurer's Guide. Because your PHB+1 is Xanathar's.
"Originally," said Amy Lynn Dzura, DDAL Community Manager, "the “PH[B] + 1” rule was established to maintain character balance, since new rules options were only being playtested with the assumption a player only possessed a Player’s Handbook," but that isn't really the case, anymore.
Their research likely shows that most players have access to the books, and want to use them. It certainly won't hurt book sales to open character options widely.
Here are the highlights from the announcement:
Player options are wide open, with some limitation, but DM items remain verboten.
There are multiple campaigns running for AL, and the rules for each are slightly different. The Plague of the Ancients seasonal campaign ins unaffected by these rules. Future seasonal campaigns will be covered, but for now, Icewind Dale is free of access to every book all at once
Legal for use in any campaign includes:
Player's Handbook
Volo's Guide to Monsters
Xanathar's Guide to Everything
Mordenkainen's Tome of Foes
Tasha's Cauldron of Everything
Campaigns set in the Forgotten Realms can use Sword Coast Adventurer's Guide
For the Masters and Historic campaigns (characters playing the high level DRW series, or just anything that isn't the current seasonal content) players can use the Genasi, Tortle, and Locathah races.
In future seasonal campaigns, any player options from the associated hardcover adventure will be legal for use.
And in the current alternate campaign, which is Eberron, you're allowed to use material from Eberron: Oracle of War, which makes sense, because the campaign would be weird if you couldn't.
Seismic changes for DDAL! And maybe, just maybe, the article hints the rules for the historic campaign will be dropping soon!