* National identity card: If you are a citizen of the United Kingdom, you can use your national identity card to travel between Scotland and Northern Ireland.
* Driver's license: If you have a valid driver's license from the United Kingdom, you can use it to travel between Scotland and Northern Ireland.
* Birth certificate: If you do not have a national identity card or driver's license, you can use your birth certificate as a form of identification. However, you will also need to present a form of photo identification, such as a passport photo or student ID.
It is important to note that the specific identification requirements for travel between Scotland and Northern Ireland may change, so it is always best to check with the relevant authorities before you travel.