A big boy letter is a pre-sale agreement in connection with a private sale of securities (such as in a PIPE transaction) not to sue over non-disclosure of material inside information that is not disclosed, entered into between two sophisticated parties. Big boy provisions may also be contained within securities purchase agreements, rather than being the subject of a separate letter agreement. Generally, a seller's request that a buyer agree to a big boy letter is a signal to the sophisticated buyer that there is likely to be material non-public information that exists concerning a security, which could give rise to a lawsuit brought by the buyer if it was not disclosed, in the absence of the letter.