What should I do with my expired passport?

Sometimes you have valid visas in the old passport that you might find use for later. Also you might need to use that passport to prove travel entry/exit dates at some immigration counter in the future.

If I can contribute as someone who used to have to verify identities on a regular basis, a passport is the most secure (and expensive) form of ID issued to the general public. An expired passport continues to be an excellent form of ID even if it's not longer usable for travel, and as quoted elsewhere here from the US State Department, it also continues to provide proof of citizenship should that be an issue. I keep all of my expired passports in various secure places, ready for use if my current one isn't available for some reason (loss, theft, in safety deposit box, etc) .

Another reason to keep all your old passports. Well if your applying for a PR in another country eg: Australia, one of the questions they ask is "Have any of the applicants visited any countries for less than 12 months in the past 10 years?". You have to document all the countries you visited in the last 10 years and provide dates!!.

There is one particular reason that I can think of to hold onto a passport with an used visa in it.

The local Chinese consulate will not grant a multiple-entry visa to first-time visitors to the country. Don't ask me why, that's just how they do it. So if you want a multiple-entry visa and you've got a passport that has no China visas in it, presenting an old passport with a cancelled visa will prove you're not a first-timer, and they'll grant the visa.

It's possible other countries have similar restrictions on the type of visas they issue.

I (almost) never take an old passport with me when I travel-- I'd worry about it disappearing and being used for nefarious purposes (my valid one is always on my person or locked in a safe). The sole case when I did, it was used for identification, and the new one has a different number so it would not do.

Sometimes for future immigration purposes, or other purposes where you have to keep track of periods of presence in a country (e.g. taxes, requirements to pass on citizenship, whatever), it's nice to be able to go back and refer to past entry and exit stamps.

The U.S. Department of State, who issue passports, recommend you keep the old one.

Yes, we will return the old, cancelled passport to you. It may be sent separately from your new passport. It is a good idea to keep your old passport in a safe place as it is considered proof of your U.S. citizenship.

Another possible reason to keep your old passports is as a continuous record of identity.

A while ago I knew someone that had trouble with passports twice - lost one, I think, and something else. In any case, when he was going to renew it the next time, there came up another problem with his birth certificate - that no one had mentioned before, not even with other passports... possibly just the extra scrutiny this time. Since there wasn't time before travel to have another copy mailed to him, he brought along all the additional proofs of identity he could, hoping to get his passport renewed in time.

This included every expired passport he had - as a continuous record, of who he is and proof that his identity was real. He had them going all the way back to childhood, because of overseas relatives. Just like an expired passport can still be used as proof of identity in some places, a record of them shows that someone's identity has history.

I don't know if the passports were the deciding factor, or if the other documents he had were enough, but they took them and looked them over (instead of being confused at him, which suggests that they can indeed be used as this sort of continuous record), and they did issue him his passport, so I guess it was helpful to have them.

I suppose it's pretty unlikely that someone would need to prove their identity in this way, or to use them to show a continual proof of identity - but it might happen, however rare, and it is probably not a bad thing to keep the old passports anyway. If something happened to your passport (or even most-recently-expired one), then having an even older one might someday be an extra kind of backup, as proof of citizenship, as one more piece of bureaucratic proof, or anything else you want it for.

In Visitor : supporting documents guide GOV.UK has five pages of documents that are either obligatory or recommended. The very first of the recommended is Previous travel documents/passports, which show previous travel.

Maybe your old passport contains no such evidence, or you will never seek to enter UK, but otherwise it may make your entry smoother.

Personally, I have found other people's old passports of interest for historical and genealogical purposes. For example, some of my mother's passports mention a middle name she never liked - and managed to get removed from a birth certificate. (I have since found another birth certificate that does show that middle name, together with some slightly different other details but have the link to prove the two certificates are for the one person.)

The revenue stamps may have some value to collectors (though these are not used nowadays, they did used to be).

One of the visas gave me the name I was seeking of the vessel that transported me across the Atlantic (at an age when I was oblivious to such things).

In summary, even if no use to you at present, they may be of interest to others, eventually. So for "What should I do with my expired passport?" I suggest, "Keep it".

However, that might not always be possible. For example David mentions:

I am French and we are not allowed to keep old passports.

... in a question where it seems retention would have been useful for the required record of previous visa details (a reason for retention already mentioned by others).

I personally staple my previous passport on the back of my current passport and leave any older ones at home. It's definitely advisable to keep them in a safe spot somewhere i.e you shouldn't dispose them.

I would recommend carrying the immediate previous passport with you as it provides more information about your identity and past travel. It is also useful in case you have any valid visas on it. If it does not carry any older visas in it you should be good just by leaving it in a safe place at home or somewhere else as well.