If you've booked a holiday to the United States, I would highly advise that you check your passport immediately for the camera logo on the cover (please see above). A number of holiday goers have been turned away from embarking on their travels due to a recent change in rules.
As of the 1st April 2016, all passengers travelling to the US on the Visa Waiver/Esta programme will need a valid e-passport which contains a microchip. If your passport doesn't meet this new criteria you will NOT be able to travel.
If you do find out that you have an older passport without a chip, you will have to apply for a new one to be permitted to travel. For any last minute applications, the Passport Office offer a premium 1 day or a fast track 1 week service to get your new passport. For more info on applying for a new passport click here.