Non-vicarious liability for the acts of third parties is distinguishable from the traditional doctrine of vicarious liability insofar as it relates to a form of primary liability predicated upon the personal fault of the defendant. More conveniently termed 'third party liability', it is a novel category of tortious liability that has evolved from a collection of disparate and isolated judicial decisions setting out, on an entirely ad hoc basis, individualised exceptions to the entrenched common law rules against liability for omissions and liability for the acts of others. As a result of the improvised nature of its development, the current law on third party liability is unstructured, unprincipled and incoherent. The specific purpose of this book is to seek out the foundational principles governing the various existing instances of third party liability, with a view to identifying a coherent legal basis upon which such liability can develop in the future.