Is hemp cultivation legal in the U.S.

Federal action
The 2014 Agricultural Act, more commonly known as the 2014 Farm Bill, includes section 7606, which allows for universities and state departments of agriculture to cultivate industrial hemp, as long as it is cultivated and used for research. Under the 2014 Agricultural act, state departments and universities must also be registered with their state, and defer to state laws and regulations for approval to grow hemp. 
As part of the Agriculture Improvement Act of 2018 (aka the 2018 Farm Bill), the Hemp Farming Act of 2018 reclassified hemp (with less than 0.3% THC) from Schedule I, the federal government's most restrictive classification of controlled substances, which are considered highly prone to abuse and without medicinal benefits. This move to federally legalize hemp allowed for its cultivation and distribution as a legal agricultural product. 
Under the Hemp Farming Act, hemp cultivation is no longer limited to state departments and universities. In addition, the act gives hemp farmers the right to water, crop insurance, and federal agricultural grants, as well as legal access to national banking. Hemp may also be transported across state lines. 
State laws
Prior to the Hemp Farming Act of 2018, 41 states had passed industrial hemp-related legislation. Thirty-nine of those states legalized statewide cultivation programs that defined hemp specifically to differentiate it from marijuana, establish licensing requirements, and regulate production. 
The Hemp Farming Act now requires state departments of agriculture to consult with their governors and chief law enforcement officers on a regulatory program, which will then be submitted to the US Secretary of Agriculture for approval. According to Section 297B of the bill, state hemp regulatory programs must include a system to maintain information on all land where cultivation takes place, procedures for testing THC levels in hemp, and procedures for disposing of products that violate THC content restrictions.