L1A visa is for multinational managers and executives. 

Managerial capacity now defined under the Immigration and Naturalization Act: an assignment with an organization in which the employee primarily:

Manages the organization, department, subdivision, function or component; Supervises and controls the work of other supervisory, professional or managerial employees, or manages an essential function within the organization or department or subdivision of the organization; Has authority to hire and fire or recommend personnel actions, or if no direct supervision, functions at a senior level within hierarchy or as to function managed and Exercises discretion over day-to-day operations of the activity or function.

Executive capacity defined under the Immigration and Naturalization Act: an assignment in an organization in which the employee primarily:

Directs the management of the organization or a major component or function; Establishes goals and policies; Exercise wide latitude in discretionary decision making and Receives only general supervision or direction from higher level executives, board of directors or stockholders.

L1B visa is for specialized knowledge professionals.

Special knowledge is defined under the Immigration and Naturalization Act: a person who has special knowledge of the company product, service, research, equipment, techniques, management or other interests and its application in international markets or has an advanced level of knowledge of processes and procedures of the company.  

  1. One year employment requirement. The beneficiary must be employed continuously abroad for one of the past three years by parent, branch, affiliate or subsidiary of U.S. company preceding his application for admission. The one year must be continuous, but it does not have to be immediately before admission.
  2. Qualifying relationship. a. majority stock ownership in both companies or b. control of the parent company or c. Ownership by common group. i.e. US company owned 1/3 by family corp. 1/3 by person who owns foreign corp. and 1/3 by family of person

Petition is generally approved for three years.

For new offices in US which are open for less than a year, the petition will only be approved for only one year.

The L1 visa can be extended to the maximum duration as follows:

For L1as, a maximum duration of 7 years.

For L1bs, a maximum duration of 5 years.

The maximum duration applies to dependents as well as the principle applicant.

Time spent in H status will be count toward the maximum duration time.