"Due diligence is essential to all deal making because it allows a party to make an informed decision as to whether it should enter into a transaction, and if so, on what terms. In a securities transaction,due diligence also ensures that public statements are not based on incorrect information and do not provide incomplete or misleading disclosure. If conducted effectively, due diligence is an extremely valuable tool for uncovering risks that can either serve as bargaining points for negotiating the terms of an agreement or as reasons to withdraw from the deal. Failing to recognize these risks can cause significant problems for a party, ranging from an unfavorable business transaction to liability and damages."
- Due Diligence Toolkit, by Practical Law Corporate & Securities
What lawyers and bankers do to learn about a company
"Diligence activities are broad and range from a review of relevant documents (often in a Data Room) and Financial Statements to plant visits and interviews with management, outside accountants, counsel, customers, and suppliers"
- Book of Jargon
"The diligence reasonably expected from, and ordinarily exercised by, a person who seeks to satisfy a legal requirement or to discharge an obligation."
"Corporations & securities. A prospective buyer's or broker's investigation and analysis of a target company, a piece of property, or a newly issued security. • A failure to exercise due diligence may sometimes result in liability, as when a broker recommends a security without first investigating it adequately"
- Black's Law Dictionary (10th ed. 2014)
The Essentials of M&a Due Diligence by 
Diagnostics for Strategic Decision-Making by 
