A bit over a year ago I applied for (and got) an ESTA for travel to the USA, valid for two years. That validity takes the ESTA to pretty close to the end of the passport validity.
I've just renewed my passport a bit early, to avoid problems with having enough passport validity on a different trip. Do I need to also get a new ESTA (for another 2 years starting today), or can I continue to travel on the existing ESTA until that expires, and only need to renew it then? (I am planning to travel to the US before the old ESTA expires)
(If you wish to travel to the US under the Visa Waiver Program, except by land, you need to to apply for an ESTA (Electronic System for Travel Authorization) before you travel.)