A Visas - Diplomats and Government Officials C1/D Visas - Crew Members & Transitory Passengers
G Visas - Employees of International Organizations
I Visas - Foreign Media Representatives
L Visas - Intracompany Transferees
O Visas - Extraordinary Ability in Sciences, Arts, Education, Business, or Athletics
P Visas - Athletes
R Visas - Religious Workers
A Visas - Diplomats and Government Officials
To qualify for an "A" visa, the individual concerned must be traveling to the United States on behalf of his or her national government to engage in official activities for that government. The fact that there may be government interest or control in a given organization is not in itself the defining factor in determining whether or not the applicant qualifies for an A visa; the particular duties or services to be performed must also be of an inherently governmental character or nature. Local government officials representing their state, province, city or other local political entity do not qualify for "A" visa status and should travel in B-1 status. This can be done either on the Visa Waiver Program (with an ESTA approval) or with a B-1 (or B-1/B-2) visa. Government officials traveling to the United States to perform non-governmental functions or traveling as tourists require a "B" visa, or, if eligible, may travel visa-free under the Visa Waiver Program.
C1/D Visas - Crew Members & Transitory Passengers
If you are transiting the U.S. en route to another foreign destination, even if you only intend to be present in the U.S. for a few hours and do not plan to leave the airport, you still need a valid visa (such as a B or C visa), or must be eligible for visa-free travel under the Visa Waiver Program.
Individual C-1/D visas are issued to crew members of international airlines and to aliens required for the normal operation and service of a vessel. In the case of the later, in determining who qualifies for the C-1/D visa, the U.S. Consulate will take into consideration the individual's responsibilities and activities on the ship. For example the most commonly issued C-1/D visas are to crew members of cruise liners and include, but are not limited to, beauticians, entertainers and lifeguards.
Dry Dock: Crewmen who are to service a vessel in dry dock require the appropriate work visa unless the work is being done under warranty in which case, they qualify for a B-1 visa.
Private Yacht: If you will be working on a private yacht sailing out of a foreign port and cruising in U.S. waters for more than 29 days, you require a B-1 visa.
Holiday: If you wish to remain in the United States for a holiday after your period of employment, you will be required to apply for admission as a visitor on a B-2 visa. However, if you enter the U.S. aboard a cruise liner which participates in the Visa Waiver Program you may be eligible to enter without a visa in your passport. You should check with the cruise liner before traveling.
Dependents of Crewmen: Dependents of crewmen (D) visa holders who are accompanying the alien to the U.S. may be eligible for B-2 visa. Note: Visa free travel under the Visa Waiver Program is only available to those who enter the United States aboard a participating carrier. Many shipping companies are not participating carriers.
G Visas - Employees of International Organizations
To qualify for a "G" visa the individual concerned must be entering the United States in pursuance of official duties. Members of a permanent mission of a recognized government to an international organization are eligible for G-1 Visas; representatives of a recognized government traveling to the United States temporarily to attend meetings of a designated international organization are eligible for G-2 visas and representatives of non-recognized or non-member governments are eligible for G-3 visas. G-4 visas are issued to individuals who are proceeding to the United States to take up an appointment at a designated international organization, including the United Nations.
NATO Visas: An individual will be classified under the symbol "NATO", if he or she is seeking admission to the United States under the applicable provision of the Agreement on the Status of the North Atlantic Treaty Organization, National Representatives and International Staff. However, many armed forces personnel are exempt from passport and visa requirements if they are either attached to NATO Allied Headquarters in the United States and are traveling on official business, or are entering the United States under a NATO Status of Forces Agreement. In the case of the later, they must carry official military ID cards and NATO travel orders.
Immediate Family Members of Diplomats/Officials, NATO Members: Immediate Family Members are defined as the spouse and unmarried sons and daughters of any age who are members of the principal applicant's household. They are eligible for a derivative visa. Cohabitating domestic partners who are recognized as the principal alien’s dependent by the sending government, while not eligible for derivative visas, may apply for B1/B2 visas, if otherwise qualified.
I Visas - Foreign Media Representatives
Representatives of the foreign media traveling to the U.S. on assignment may be eligible for classification under the I-visa category. This may include members of the press, radio, film or television whose activities are essential to the foreign media function, such as reporters, film crews, editors and persons in similar occupations. Please note that only those who are actually involved in the newsgathering process are eligible (proof readers, librarians, or set designers are not eligible).
Freelance journalists and members of independent production companies will also be considered for an I-visa if they are under contract to a media organization.
Persons engaged in the production or distribution of film only qualify for an I-visa if the material being filmed will be used to disseminate information or news, and the primary source of funding and point of distribution will be outside the US. All published material must be documentary in nature.
Individuals or companies commissioned to work on film projects of commercial or entertainment value require the appropriate work visa (O, P or H), which involves obtaining employment authorization from the U.S. Citizenship and Immigration Services (USCIS) before applying for a visa.
I-visas are also appropriate for foreign journalists working for an overseas branch, office, or subsidiary of a US network, newspaper, or other media outlet if the journalist is going to the US to report on US events solely for a foreign audience. If the journalist will replace or augment American journalists reporting on US events for an American audience, a work visa will be required.
Temporary Workers (H/L/O/P Visas) 
Working in the United States is only possible with a visa - regardless of how long or short you stay. To receive a work visa, a U.S. employer has to file a petition for a work permit for you in the U.S. After the petition has been approved you can apply for a visa. U.S. immigration laws prohibit you from taking a summer job, accepting an internship or au pair position if you do not have the proper visa. You may not enter the States on a tourist visa and then search for a place to work or do an internship.
The Immigration and Nationality Act provides several categories of nonimmigrant visas for a person who wishes to work temporarily in the United States. There are annual numerical limits on some classifications.
H-1B classification applies to persons in a specialty occupation, which requires the theoretical and practical application of a body of highly specialized knowledge requiring completion of a specific course of higher education. This classification requires a labor attestation issued by the Secretary of Labor. Government-to-Government research and development, or co-production projects administered by the Department of Defense also apply to this classification;
H-2A classification applies to temporary or seasonal agricultural workers;
H-2B classification applies to temporary or seasonal nonagricultural workers. This classification requires a temporary labor certification issued by the Secretary of Labor;
H-3 classification applies to trainees other than medical or academic. This classification also applies to practical training in the education of handicapped children;
L-1 classification applies to intra-company transferees who, within the three preceding years, have been employed abroad continuously for one year, and who will be employed by a branch, parent, affiliate, or subsidiary of that same employer in the U.S. in a managerial, executive, or specialized knowledge capacity (there is a $500 "fraud prevention and detection fee" for persons applying for L-1 visas under "blanket" provisions abroad);
O-1 classification applies to persons who have extraordinary ability in the sciences, arts, education, business, or athletics, or extraordinary achievements in the motion picture and television field;
O-2 classification applies to persons accompanying an O-1 alien to assist in an artistic or athletic performance for a specific event or performance;
P-1 classification applies to individual or team athletes, or members of an entertainment group that are internationally recognized;
P-2 classification applies to artists or entertainers who will perform under a reciprocal exchange program;
P-3 classification applies to artists or entertainers who perform under a program that is culturally unique (same as P-1); and
Family Members: With the exception of "Q-1 Cultural Exchange Visitors," the spouse and unmarried, minor children of an applicant under any of the above classifications may also be classified as non-immigrants in order to accompany or join the principal applicant. With the exception of spouses of L visa "inter-company transferees", a person who has received a visa as the spouse or child of a temporary worker may not accept employment in the United States. The principal applicant must be able to show that he or she will be able to support his or her family in the United States.
Time Limits: All of the above classifications have fixed time limits in which the alien may perform services in the United States. In some cases U.S. Citizenship and Immigration Services (USCIS) may extend those time limits in order to permit the completion of the services. Thereafter, the alien must remain abroad for a fixed period of time before being readmitted as a temporary worker under any classification. The USCIS will notify the petitioner on Form I-797 whenever a visa petition, an extension of a visa petition, or an extension of stay is approved under any of the above classifications. The beneficiary may use form I-797 (original) to apply for a new or revalidated visa during the validity period of the petition. The approval of a permanent labor certification or the filing of a preference petition for an alien shall not be a basis for denying a visa under the H-1 or L classifications.
R Visas - Temporary Religious Workers
The Immigration and Nationality Act provides a nonimmigrant visa category "R" for aliens proceeding to the United States to work in a religious capacity. Religious workers include ministers of religion who are authorized by a recognized denomination to conduct religious worship and perform other duties usually performed by members of the clergy such as administering the sacraments, or their equivalent. The term does not apply to lay preachers. A religious vocation means a calling to religious life, evidenced by the demonstration of a lifelong commitment, such as taking vows. Examples include nuns, monks, and religious brothers and sisters. A religious occupation means a habitual engagement in an activity which relates to a traditional religious function. Examples include liturgical workers, religious instructors or cantors, catechists, workers in religious hospitals, missionaries, religious translators, or religious broadcasters. It does not include janitors, maintenance workers, clerks, fund raisers, solicitors of donations, or similar occupations. The activity of a lay-person who will be engaged in a religious occupation must relate to a traditional religious function: i.e., the activity must embody the tenets of the religion and have religious significance, relating primarily, if not exclusively, to matters of the spirit as they apply to the religion.
Applying for the Visa: Religious workers should generally apply at the U.S. Embassy or Consulate with jurisdiction over their place of permanent residence. Although visa applicants may apply at any U.S. consular office abroad, it may be more difficult to qualify for the visa outside the country of permanent residence. As part of the visa application process, an interview at the embassy consular section is required for visa applicants from age 14 through 79. Persons age 13 and younger, and age 80 and older, generally do not require an interview, unless requested by embassy or consulate. The waiting time for an interview appointment for applicants can vary, so early visa application is strongly encouraged. Visa wait times for interview appointments and visa processing time information for each U.S. Embassy or Consulate worldwide is available on our website at Visa Wait Times, and on most embassy websites. During the visa application process, usually at the interview, an ink-free, digital fingerprint scan will be quickly taken. Some visa applications require further administrative processing, which takes additional time after the visa applicant's interview by a Consular Officer. There is no requirement that applicants for "R" visas have a residence abroad that they have no intention of abandoning, but they must intend to depart the United States at the end of their lawful status.
Family Members: A nonimmigrant religious worker's spouse and unmarried children under 21 years of age may be granted derivative status. They may study but may not accept employment in the United States.
Time Limits: Holders of R visas may remain in the U.S. for up to five years to pursue their calling.
GENERAL NOTE: A visa allows a foreign citizen coming from abroad, to travel to the United States port-of entry and request permission to enter the U.S. Applicants should be aware that a visa does not guarantee entry into the United States. The Department of Homeland Security, U.S. Customs and Border Protection (CBP) officials have authority to permit or deny admission to the United States. If you are allowed to enter the U.S., the CBP official will determine the length of your visit on the Arrival-Departure Record (Form I-94). Since Form I-94 documents your authorized stay in the U.S., it’s very important to keep in your passport. In advance of travel, prospective travelers should review important information about Admissions/Entry requirements, as well as information related to restrictions about bringing food, agricultural products or other restricted/prohibited goods explained on the Department of Homeland Security, Customs and Border Protection website. Upon arrival (at an international airport, seaport or land border crossing), you will be enrolled in the US-VISIT entry-exit program. In addition, some travelers will also need to register their entry into and their departure from the U.S. with the Special Registration program.