What is the async pipe in Angular?

The async pipe subscribes to an Observable or Promise and returns its latest emitted value. When the component is destroyed, it automatically unsubscribes from the Observable — preventing memory leaks without manual subscription management. With Observable: // Component: users$ = this.userService.getUsers(); // Template: <ul><li *ngFor="let user of users$ | async">{{ user.name }}</li></ul>. With null check: <div *ngIf="user$ | async as user">{{ user.name }}</div> — the "as" syntax assigns the emitted value to a local template variable, preventing multiple subscriptions. With loading state: <ng-container *ngIf="users$ | async as users; else loading"> <app-user-list [users]="users"></app-user-list> </ng-container> <ng-template #loading><app-spinner></app-spinner></ng-template>. Benefits over manual subscribe: (1) Auto-unsubscribes on destroy; (2) Triggers change detection on new values; (3) Works naturally with OnPush change detection strategy (manual subscribe + property assignment won't trigger OnPush). Multiple uses: using users$ | async multiple times in the same template creates multiple subscriptions. Use the "as" syntax or shareReplay(1) to share one subscription. Async pipe in OnPush: one of the key reasons to use async pipe — it correctly marks the component for check when Observable emits.