Nationals of Canada and Mexico may take advantage of this special visa category created by the North American Free Trade Agreement.
The TN is available to those sponsored by an employer to perform work in the U.S. which is included in a list of occupations that is part of the treaty. Most importantly, the foreign national must be a citizen of either Mexico or Canada to qualify.
The TN has the advantage that it may be available for some positions that may not qualify under the CIS' definition of specialty occupation which is a requirement for the H-1b. Canadians are not required to comply with the prevailing wage requirement and other requirements associated with the Labor Condition Application, while Mexican nationals are required to comply with the requirements of the LCA.
The procedures for applying are also greatly streamlined which allow a foreign national to begin work much more quickly.