Are Shimano and SRAM compatible?

At 11s the chain and cassette are interchangeable, but the shifter and derailleur must be the same brand (different cable pull). At 12s the systems are separate: SRAM Flattop/XDR vs Shimano Hyperglide+.

Compatibility by speed: the table

What you can mix between Shimano, SRAM and Campagnolo depending on the number of speeds.

Speeds	Chain & cassette across brands	Shifter + derailleur
8 / 9 / 10s	Shimano and SRAM largely interchangeable (same chain pitch).	Same brand recommended.
11s road	Shimano / SRAM / KMC chain and cassette interchangeable. Campagnolo separate.	MUST be same brand: different cable pull.
12s road	NO: SRAM (Flattop + XDR), Shimano (Hyperglide+) and Campagnolo are separate systems.	Same brand / system.
12s MTB	NO: Shimano Micro Spline vs SRAM Eagle (XD) are separate systems.	Same brand / system.

The golden rule (3 points)

Chain → match it to the speed (8/9/10/11/12s: different widths).
Shifter + derailleur → same brand (Shimano, SRAM and Campagnolo have different cable pull, they don't mix).
Cassette → it must sit on the right freehub body (HG / XD / XDR / Micro Spline / N3W). See by brand →

Indicative data — always check the manufacturer's official specs.