How does Cross-Program Invocation work?

Each Cross-Program Invocation (CPI) instruction must specify the following information:

Program Address or ID: The identifier of the program being called.
Account List: Every account that the instruction reads from or writes to, including accounts of other programs.
Instruction Data: Specifies which instruction on the program to invoke.

flowchart TD
    CPI[Each CPI Instruction]
    PA[Program Address or ID]
    AL[Account List]
    ID[Instruction Data]
    INV[invoke]
    INV_SIGNED[invoke_signed]

    CPI --> PA
    CPI --> AL
    CPI --> ID
    CPI -.-> INV
    CPI -.-> INV_SIGNED

    INV -->|Passes through the original transaction signature| CPI
    INV_SIGNED -->|Allows your program to sign the transaction| CPI

CPIs are made using the invoke and invoke_signed functions from the solana_program crate:

invoke: Passes through the original transaction signature.
invoke_signed: Allows your program to sign the transaction.

For an overview of CPIs, see the Overview of CPI.
For a detailed guide on implementing CPIs using Anchor, see Cross-Program Invocations in Solana Using Anchor.
For key features of CPIs, see Key Features.
For reasons to use CPIs in your projects, see Why Use Cross-Program Invocation.
For practical examples and use cases of CPIs, see Examples of CPI.
For a step-by-step tutorial on implementing CPIs, see the Tutorial on Cross-Program Invocation.