Check the conditions before filling the ESTA Application.

Do I need to apply for ESTA.

I am a national of Canada.
No, nationals of Canada who are travelling with a Canadian travel permit do not need an ESTA.

I am a Landed Immigrant of Canada
If you are a landed migrant of Canada and a national of a country that takes part in the Visa Waiver Program (VWP), and you enter the U.S. via land, ESTA is not required. If you do not have ESTA, you will be required to complete an I-94W and continue through a manual section process at the area fringe crossing. In case you have an affirmed ESTA when entering the U.S. at an area outskirt crossing, you won't be required to finish the I-94W e and your entry will be permitted. If you are travelling to the U.S. via air or ocean, you DO need to apply for ESTA. If you are not a subject of a VWP country, you are required to have a visa, and in this manner, ESTA does not make a difference to you.

I am a Lawful Permanent Resident of the United States and a subject of a VWP country
No.

I am a citizen of a VWP country and am going to the U.S. from Canada or Mexico?
If you are a resident of a country that participates in the Visa Waiver Program (VWP), and you enter the U.S. via land from Mexico or Canada, ESTA is not required. If you do not have ESTA, you will be required to complete an I-94W and continue through a manual section process at the area outskirt crossing. If you have an affirmed ESTA when entering the U.S. at an area fringe crossing, you won't be required to complete an I-94W, and your entrance procedure is accelerated. Nonetheless, if issued, you ought to return your green I-94W card upon takeoff from the U.S. If you are landing via air or ocean, you do need to apply for ESTA.

I am a national of a VWP country and am setting out to the United States via air to travel the U.S.
Yes. You should apply for ESTA regardless of the possibility that you are just travelling to the U.S. In the location field of the application, select "In Transit."

I have dual citizenship from both a VWP country and a non-VWP country.
If you are flying under the terms of the VWP, with your VWP visa, you should apply for ESTA. If you are utilising your non-VWP country's passport, you will require a visa and ESTA has no importance to you.

I am a national of a VWP country and am travelling to Guam or the Commonwealth of the Northern Mariana Islands (CNMI)?
For universal travel to Guam/CNMI under the VWP, ESTA is required. Nationalities that are qualified for Guam/CNMI VWP can travel to Guam/CNMI under that program without an ESTA. In any case, under the Guam/CNMI VWP, the longest stay is 45 days and the stay is limited to only those islands – travel can not be to the United States.
Travelling from the United States to Guam/CNMI is viewed as a household flight, so no ESTA is required. Travellers experience pre-examination for travel from Guam/CNMI to the United States. If travel is under VWP, an ESTA is required.

I am a national of a VWP country and am travelling for transient business or tourism under the VWP to Puerto Rico or the U.S. Virgin Islands?
Yes, ESTA is required to visit these locations.

I am travelling with a minor (kid under age 18) who is a subject of a VWP country?
If the minor is making a trip to the United States under the VWP as a vacationer for 90 days or less, he/she is required to obtain a free ESTA endorsement.

I am a U.S. National with dual citizenship from a VWP country?
U.S. Nationals are not required to have an ESTA and are required to utilise their U.S. visa to travel to the U.S.

In the event, I have a present and valid visa? People who have a valid visa will have the opportunity to travel to the United States on the visa for the reason in which it was issued. People travelling on substantial visas are not required to apply for an ESTA approval.