*Note:* Long Payment IDs have been removed since release 0.15; it's not possible to use them anymore. More info in the [blog post](https://getmonero.org/2019/06/04/Long-Payment-ID-Deprecation.html) that announced their deprecation.
Payment ID is an **arbitrary** and **optional** transaction attachment that consists of 32 bytes (64 hexadecimal characters) or 8 bytes (in the case of integrated addresses).
The Payment ID is usually used to identify transactions to merchants and exchanges: Given the intrinsic privacy features built into Monero, where a single public address is usually used for incoming transactions, the Payment ID is especially useful to tie incoming payments with user accounts.
### Compact Payment IDs and Integrated Addresses
Since the 0.9 Hydrogen Helix version, Payment IDs can be encrypted and embedded in a payment address. The Payment IDs of this type should be 64-bits and are encrypted with a random one-time key known only to the sender and receiver.
### Creating a Payment ID
It is recommended to use the official wallet's `integrated_address` command to automatically generate Integrated Addresses that contain Compact Payment IDs. If you want to use the command line, you can generate Payment IDs as follows:
Creating a compact Payment ID for an Integrated Address:
