> ## Documentation Index
> Fetch the complete documentation index at: https://hedera-0c6e0218-mintlify-bc559771.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# TopicID

> TopicID is the Hedera protobuf identifier for a Hedera Consensus Service topic, addressed by shard, realm, and topic number for message submission.

Unique identifier for a topic (used by the consensus service)

| Field      | Description                                           |
| ---------- | ----------------------------------------------------- |
| `shardNum` | The shard number (nonnegative)                        |
| `realmNum` | The realm number (nonnegative)                        |
| `topicNum` | Unique topic identifier within a realm (nonnegative). |

#### <a href="#undefined" id="undefined" />