A non-disclosure agreement (NDA) or a non-disclosure term in a contract protects against an information shared with a contracting party getting disclosed to a third person. The clause is also called a confidentiality agreement or secrecy agreement. A non-disclosure agreement has come to be tied with a restraint of trade agreement. In this agreement, an employee undertakes restraints on his activities after leaving the employment. It also applies to a vendor selling his business and goodwill; and exclusive trade relationships. The common law principle is unless the restraint on trade is reasonable, it is void. The chapter explores the validity and nature and structure of a non-disclosure agreement; and the principles developed by the courts to test the reasonableness of a restraint of trade and to severe void restrains from the others.