# SIP API

> \[!NOTE]
>
> Looking for a quick introduction to our SIP offering, check out the [SIP Quickstart](/docs/voice/sip/quickstart)

Session Initiation Protocol ([SIP](/docs/glossary/what-is-session-initiation-protocol-sip)) is a signaling protocol for initiating, terminating and modifying user sessions over an IP network. Most commonly, SIP is used in Voice Over IP (VoIP) services but is also often used for other communications sessions such as video calls and instant messaging sessions.

Explore Twilio's SIP resources:

* [SIP Credential Resource](/docs/voice/sip/api/sip-credential-resource)
* [SIP CredentialList](/docs/voice/sip/api/sip-credentiallist-resource)[Resource](/docs/voice/sip/api/sip-credentiallist-resource)
* [SIP CredentialListMapping](/docs/voice/sip/api/sip-credentiallistmapping-resource)[Resource](/docs/voice/sip/api/sip-credentiallistmapping-resource)
* [SIP Domain](/docs/voice/sip/api/sip-domain-resource)[Resource](/docs/voice/sip/api/sip-domain-resource)
* [SIP Domain Registration CredentialListMapping Resource](/docs/voice/sip/api/sip-domain-registration-credentiallistmapping-resource)
* [SIP IpAccessControlList Resource](/docs/voice/sip/api/sip-ipaccesscontrollist-resource)
* [SIP IpAccessControlListMapping Resource](/docs/voice/sip/api/sip-ipaccesscontrollistmapping-resource)
* [SIP IpAddress Resource](/docs/voice/sip/api/sip-ipaddress-resource)