is when one party is held legally responsible for the actions of another party. There are generally two kinds of secondary liability
– vicarious liability
and contributory liability
Vicarious liability arises under the common law doctrine of agency – respondeat superior – the responsibility of the superior for the acts of their subordinate and can be distinguished from contributory liability, which is rooted in the tort theory of enterprise liability.
Vicarious liability can generally be established where the third party has the right, ability, or duty to control the actor. Thus, an employer can be found vicariously liable for the acts of an employee (particularly if the act is in the course of employment) or a parent can be found vicariously liable for the acts of a child. The key elements for contributory liability on the other hand are knowledge and material contribution to (or enabling of) the act itself.
Vicarious liability attributes the act itself to the third party (as if the conduct were the act of that third party) by virtue of the relationship with the actor whereas contributory liability holds the third party liable for the primary act by virtue of the third party's relationship with the actual harm (either by enabling it or benefiting from it).
Liability of ISPs
The issue of whether Internet service providers
(ISPs) should be held liable for the actions of network users is unresolved.  However, ISPs remain liable, in all territories, as primary, direct infringers of copyright
for the copies they make on behalf of their customers, so the question of whether they may additionally on occasion be secondarily liable is not very significant. An ISP's direct liability arises from the ISPs own actions; not the actions of another party, though it is often mistakenly said to. The confusion arises from the fact that two parties are directly liable in the usual case of internet infringement: the ISP and the ISP's customer. In legal terms, they are joint tortfeasors. This is because they each, independently commit all of the acts necessary to establish liability under the copyright laws of most countries. In situations truly involving secondary liability, the party for whom secondary liability is claimed has not committed at least one element required for an infringement action. This situation is not present in the usual ISP situation, as the ISP always is in the position of making copies (without authorisation of the rightsowner), so it is irrelevant that someone else may have been an earlier, independent infringer of the same copyright. The ISP's liability is direct, not derivative. It is based on the ISP's own actions, not on someone else's.
Recent statutes in the USA (Digital Millennium Copyright Act of 1998) and the European Union (Directive on Electronic Commerce) have provided significant, though not total, immunity from the primary copyright liability that, in the absence of those statutes, exists for ISPs. 
 See K. A. Taipale, " Secondary Liability on the Internet: Towards a Performative Standard for Constitutive Responsibility
" (Feb. 2003).
 See D. Panethiere, "The Basis for Copyright Infringement Liability: The Law in Common Law Jurisdictions," 13 European Intellectual Property Review 26 (1998).