This collection of essays investigates the way in which modern private law apportions responsibility between multiple parties who are (or may be) responsible for the same legal event. It examines both doctrines and principles that share responsibility between plaintiffs and defendants, on the one hand, and between multiple defendants, on the other. The doctrines examined include those 'originating' doctrines which operate to create shared liabilities in the first place (such as vicarious and accessorial liability); and, more centrally, those doctrines that operate to distribute the liabilities and responsibilities so created. These include the doctrine of contributory (comparative) negligence, joint and several (solidary) liability, contribution, reimbursement, and 'proportionate' liability, as well as defences and principles of equitable 'allowance' that permit both losses and gains to be shared between parties to civil proceedings. The work also considers the principles which apportion liability between multiple defendants and insurers in cases in which the cause, or timing, of a particular loss is hard to determine. The contributions to this volume offer important perspectives on the law in the UK, USA, Canada, Australia and New Zealand, as well as a number of civilian jurisdictions. They explicate the main rules and trends and offer critical insights on the growth and distribution of shared responsibilities from a number of different perspectives – historical, comparative, empirical, doctrinal and philosophical.