美国分哪几种签证？
根据美国移民局和海关及边境保护局的定义，赴美签证主要有四类： 1)非移民类签证(Non-immigrant Visas);2)移民签证(Immigrant Visa;3)回美证(Reentry Permit)；4)美国公民亲属绿卡优先(CRP)。其中，前三种是赴美签证的主要类型，第四种相对小众一些。以下将结合这些签证的具体类别进行详细介绍。
一、非移民签证 (NON-IMMIGRANT VISA)： 1. B-1/B-2签证（旅游/探亲）： 这是一种最常见的美国短期访问签证[1]，适合赴美的游客或其来访的亲人申请。此签证分为两类：B-1签证适用于商务旅行者，包括参加商业会议或短期工作等；而B-2签证则专指来美进行短期的观光度假，或拜访亲友的旅客持有这种签证入境时并不受限制，但在入境时可能会被问询入境目的以做记录。如果被问到的目的与所持签证目的不符，就有可能会被拒绝入境。B-1和B-2可合称为“B”字签证或者“访问签证”(visitor's visa) 根据申请者不同，此类签证有效期从1年至10年不等。在有效期内可以多次往返于美国和原居住地之间。
2. F-1学生签证F-1： This is a non-immigrant student visa available to people seeking full-time study at an American college or university. Students who are on this type of visa must be enrolled in an approved educational institution for the entire duration for which they have been authorized， participate in academic courses and remain legally in the US after classes end each day. They need to leave the country before any period exceeds their authorized stay unless they can secure approval from USCIS for additional time in the U.S. This authorization usually applies to students up to six months beyond their school program， but it may vary depending upon how long your education takes. The validity periods for different types of visas range from one year to ten years depending upon what category you fall under. If you plan to attend high school in the United States rather than college， you will most likely need to apply for an M-1 visa if studying at an elementary level requires more than two semesters of instruction. You might want to consider getting a dual status visa that allows for both classroom teaching and practical experience in a professional setting so as to acquire skills necessary for employment after graduation. Such a visa is called an M-189 or M-276A. To learn about specific criteria for obtaining various forms of F-1 visas please visit our page here： URL /f-1-student-visa/#What_is_an_F-1_Visa It should be noted that although there are many legitimate colleges and universities across America， not every unaccredited degree