Since 1986 citizens of certain countries do not require a visa to enter the U.S. anymore. They now have the possibility to travel under the so-called Visa Waiver Program (VWP) that allows them to enter the U.S. as a tourist for a maximum of 90 days a year, or transit the U.S. To a very limited extent the VWP can also be used for business travel ("Business Visa Waiver"), e.g. fairs, meetings, conferences etc. All business travel beyond that, such as maintenance, installation, consulting, setting up a US company, or starting employment, is no longer covered by the program, even if the stay does not exceed 90 days. In those cases it is advisable to apply for a B-1/B-2 Visa.
Quite frequently, it can be difficult to determine whether you can travel under the VWP or will have to apply for a visa. Each individual situation with all its determining factors (like travel frequency, length of the stay and purpose of the stay) has to be considered separately to determine what exactly is best for the individual traveler. Of course, we will be happy to advise you.