Under New York law, a plaintiff seeking to establish a cause of action for aiding and abetting a breach of fiduciary duty must show: “(1) the existence of a ... violation by the primary (as opposed to the aiding and abetting) party; (2) ‘knowledge’ of this violation on the part of the aider and abettor; and (3) ‘substantial assistance’ by the aider and abettor in the achievement of the primary violation.” Samuel M. Feinberg Testamentary Trust v. Carter, 652 F.Supp. 1066, 1082 (S.D.N.Y.1987) (quoting IIT v. Cornfeld, 619 F.2d 909, 922 (2d Cir.1980)).

As you might expect, this type of claim often comes up in the context of tortious interference, whereby the defendant, a third party, supposedly induced without justification (or through wrongful means) someone to breach their contract - or prospective contract - with the plaintiff. (For more information on that topic, please see "How to Prove Tortious Interference Under New York law."

To that end, there is a distinct advantage to the aiding and abetting claim over the tortious interference claim: 

Unlike the tortious interference claim, the aiding and abetting claim does not require any showing that the defendant acted without justification or through wrongful means.