How often can you enter the USA with an ESTA?

The number of possible entries is not exactly indicated on the ESTA form. Many tourists think that they can enter unlimited often. But that's not right in this form. Who wants to abuse this possibility to a permanent stay in the USA, can also be prevented from entering the country.

The border official decides on entry

With an ESTA permit, the tourist may enter the country up to 90 days within the validity period (i.e. two years) as often as desired. However, the ESTA does not entitle you to permanent residence. So anyone who leaves the USA and already enters the country the next day can have problems with the border official. Many tourists think that with an ESTA permit, entry to the USA is safe. But that's not the case. If the border official finds in the documents that the last departure was only a few days or even hours ago, he can refuse entry. There are no precise regulations on how long you have to stay in your own country in order to re-enter. It is important not to misuse the ESTA as an immigration document. Those who really want to enter the USA several times in a row have to justify this to the border official.  

Reasons for entry with an ESTA application

You can enter with an ESTA application for 90 days. A longer stay is not possible. Possible are only tourist stays and business trips. 
As a tourist, the traveller can marvel at the many sights of the USA, drive on the endless roads or try out all the fast food restaurants. Medical treatment is also possible with ESTA approval. A school attendance or a study is not possible with the ESTA.
A business trip does not mean that the traveller is allowed to stay in the USA. If you want to do that, you need a work visa. However, he may attend conferences and meetings. The exploration of business opportunities is also conceivable. Who has entered to a conference and after four weeks is a new conference, should get hardly problems  
However, if you make a round trip through the USA, leave the country for a short time and then fly back to the USA, you can be rejected by the border official

This is the best way to enter the USA

As the entry frequency with the ESTA application is not exactly regulated, there is great confusion about it. In principle, however, it is quite simple: Those who adhere to the entry conditions mentioned hardly make any mistakes. A normal holiday trip lasts hardly more than 90 days. If you want to stay longer, you should get an appropriate visa. The same also applies to hospital stays or medical treatment.
Those who travel to conferences or congresses can usually prove this well. There shouldn't be any problems. It is optimal if the tourist has booked the return flight and proves that he or she is willing to leave the country