The two types of employees who are eligible for L1 visas:
Managers and Executives
The rules of who falls into this category are quite strict and it is required that the company includes detailed description of their position and duties in the application. The manager or executive should have the role of a supervisor for professional staff, a department or a subdivision of the company. This group may get extensions on their L1 visa for up to seven years.
Specialized Worker
This category includes such workers, who have intimate knowledge of the company's proprietary techniques, systems, procedures, products or services. Such specialized knowledge staff may get extensions on their L1 visa for up to 5 years.
After expiration of the maximum period the employee must work outside the US for at least one year before being allowed to apply for a new L1 visa.