This nonimmigrant classification applies to people who wish to perform services in a specialty occupation, services of exceptional merit and ability relating to a Department of Defense (DOD) cooperative research and development project, or services as a fashion model of distinguished merit or ability.
Family members of the H-1B foreign worker are admitted to the United States in the H-4 category. Qualifying family members include only the spouse and unmarried children under 21 years old. H-4 dependents are admitted for the same period of time for which the H-1B foreign worker is admitted. H-4 dependents may alternatively be admitted in other nonimmigrant categories for which they qualify. H-4 dependents may undertake studies while remaining in the H-4 category, however, they may not engage in any form of employment.
The H-2B visa category is used by U.S. employers to temporarily employ skilled or unskilled foreign nationals in nonagricultural positions for which the employer has a temporary need and for which qualified U.S. workers are unavailable. The company must plan to employ the foreign nationals for a temporary period and the employer’s need for the skills of the foreign nationals must also be temporary. In addition, the employer must seek a “labor certification” from the U.S. Department of Labor (DOL) certifying that:
U.S. Citizenship and Immigration Services (USCIS) Director León Rodríguez announced today that, effective May 26, 2015, the Department of Homeland Security (DHS) is extending eligibility for employment authorization to certain H-4 dependent spouses of H-1B nonimmigrants who are seeking employment-based lawful permanent resident (LPR) status. DHS amended the regulations to allow these H-4 dependent spouses to accept employment in the United States.

I have finished my first review of H-4 EAD Regulations (effective 26 May 2015). Here are the takeaway points: