Electronic signature came into legal existence in the US with the passage of the United States Electronic Signatures in Global and National Commerce Act, known more commonly as ESIGN and the Uniform Electronics Transactions Act (UETA).
These laws specify that – no contract, signature or record shall be denied legal effect solely because it is in electronic form.
ESIGN is the US Federal law that established the validity of electronic signature, while the UETA is a uniform act that has been adopted as law in 47 states, the District of Columbia and the U.S. Virgin Islands.
The 3 states that did not adopt the UETA (Illinois, New York and Washington) passed their own state laws that gave electronic signatures legal status.
Please note that there are some documents types where an electronic signature may not be appropriate.  Some examples in the US where electronic signatures are not permissible include, Wills and Trusts and Powers of Attorney.  Please consult your legal counsel in order to validate which documents types may not support electronic signature.