Ethereum’s transition to proof-of-stake is like changing the engine of a moving car, where the car is the execution layer (EL) that processes the data and transactions and the engine is the consensus layer (CL) that determines how the transactions are built into blocks to make the chain. Because of this, Ethereum has execution clients (currently a choice of four) and consensus clients (currently a choice of five) that can be mixed and matched to enable security of the chain.