Monographs about tort law seem never to have been in short supply. Occasionally, authors produce theoretical books that deal with the subject as a whole. Yet much more common are those that examine some particular aspect or area of tort law, such as negligence, nuisance, product liability, defamation, or the economic torts. Until recently, one such book has been conspicuous by its absence; but Sarah Green and John Randall have now plugged that gap by rising to arguably the most unenviable challenge in tort law scholarship and writing The Tort of Conversion.

Their opening claim, that such a book is “long overdue” (p. 1) would scarcely be doubted by academics or practitioners. But can just one book meet the needs of both? After all, most practitioners are likely to want a reliable, comprehensive, expository guide to the law (with occasional critique of controversial or errant judgments) while academics interested in conversion are more likely to be drawn to the fascinating peculiarities of the this tort's evolution, or its strict liability basis and quasi-proprietary nature (which together pose interesting questions for much modern tort theory). Happily, Green and Randall's splendid book caters splendidly for both (even if a widespread undergraduate readership might be a little too much to hope for given the relative infrequency with which conversion is taught these days).

For the practitioner there is detailed analysis of all the leading cases (and many others besides), methodical navigation through the remedies maze created by the Torts (Interference with Goods Act) 1977, and a clear description of the connections and distinctions between this tort and both the economic torts (in chapter 6) and the other modern chattel torts (in chapter 3). There is also a scrupulous exposition of who may possess title to sue together with an account of the relativity of title in English law (in chapter 4). Accordingly, no practitioner using this book should now be confused as to which tort may be invoked and where, or as to what remedies will be available in any given circumstances. Furthermore, the detailed index and meticulous cross-referencing, both within and between chapters, should help ensure that anyone using this book for practical purposes will not overlook anything of significance.

For the academic, things are even better. In part, this is because chapter 2 – in an object lesson in legal history – supplies a thoroughgoing analysis of the tort's genesis and evolution. But by far the most theoretically engaging chapter is chapter 5 which deals with the subject matter of conversion. The burden of the chapter is to unpick and answer the difficult question concerning the kinds of property to which this tort can applied and which divided the House of Lords 3 to 2 in OBG v. Allan [2007] UKHL 21. The majority in that case based their answer on the fact that conversion emerged from the ancient action for trover – which was premised on a notional losing and finding of personal property. As such, they thought, it would be inapt to extend conversion to intangible forms of property which, of course, cannot be lost and found in any meaningful sense. By contrast, Lord Nicholls and Baroness Hale (in the minority) preferred a more progressive approach, according to which intangible property would be protected by conversion on the basis that intangible property is no less worthy of tort law's protection than tangible forms of wealth.

In addressing the self-same question, Green and Randall take as their starting point neither the practical dictates of the modern commercial world nor the (highly questionable) appropriateness of keeping the tort tethered to an outlived legal fiction which insists on the capacity for a thing to be lost and found. Rather, they begin by from the definition of conversion proffered in chapter 3, and which they carefully teased out of the leading cases: that conversion is a tort which “protects the current superior possessory interest in personal property” (p. 46). From this premise, they then simply address the two material questions posed by this definition: namely, whether various kinds of intangible and quasi-intangible assets are capable of being (i) aptly described as property and (ii) possessed in a legally meaningful way. On this approach, they are able to reach the same conclusion as the minority in OBG, but without flying so overtly in the face of existing authority. By showing that what the ancient cases materially reveal is the capacity for possessory rights to exist in a thing, rather than the ability of that thing to be lost and found, they do no violence to the existing body of case law.

Furthermore, their eminently sensible approach has the distinct advantage of enabling them to tackle a range of related questions that have dogged academics and courts elsewhere in the Common law world for years, such as whether money, digitised products (such as software) and body parts can properly be made the object on action for conversion. On each of these issues – as well as the one concerning intangible property – the authors' answers are both elegant and lawyerly. The elegance derives from their concise systematic approach, while the lawyerliness inheres in the careful supporting of arguments by reference to a range of persuasive judgments in other common law jurisdictions.

Of course, there will be those conservatively minded “purists” to whom this chapter will appear heretical. They will no doubt advert to what was actually decided in relation to intangible property in OBG v. Allen and (in line with the majority) possibly also argue that using conversion to protect intangible property is like using chopsticks to eat soup. They may even say that some of the questions – which have never yet troubled the English courts – have been answered by the authors on a purely speculative basis. However, Green and Randall were surely wise not to adopt an ostrich approach to these as-yet-unresolved matters. Despite its considerable antiquity, conversion remains an important modern-day tort as OBG and the protracted Kuwait Airways v. Iraqi Airways litigation amply demonstrate. Their book is, therefore, all the stronger for its provision of a carefully crafted set of answers to these seemingly inevitable questions for the future.

Like the authors of all the best pioneering books, Green and Randall will not have had the final word on conversion's nature and domain; and this is a good thing. For too long and by too many, conversion has been largely overlooked. But now there is a book to reckon with. For all that it may be a fairly slender volume, The Tort of Conversion is packed with learning, containing as it does mini-theses on the true gist of conversion, the nature of property and the legal meaning of possession. Throughout – though slightly less so in relation to the nature of property – the arguments are supported by a wealth of references to primary and secondary legal sources, both ancient and modern, domestic and comparative. There are, in consequence, very few criticisms that one may fairly make of this book without transgressing the fine line between providing an objective review of this book, and suggesting the contents of a rather different book that one would have written oneself. That said, there was one striking oddity that should perhaps be noted. It was that, although the book contained specific discussion of the overwhelmingly irrelevant partial defence of contributory negligence to which there is only one very minor exception (p. 206), there was no equivalent detailed guide to the complex rules on limitation of actions in cases of conversion set out in sections 3, 4 and (in the case of concealed fraud) 32 of the Limitation Act 1980. But this was just one blip in an otherwise comprehensive and eminently readable account of the law of conversion.

It may be a very long time before we can disagree conclusively with Sir John Salmond's famous observation that “conversion is a region still darkened with the mists of legal formalism, through which no man will find his way” or Baron Bramwell's quip that “no one can undertake to define what a conversion is”. But if a way out of this juridical quagmire is ever to be forged, Green and Randall, in this superb volume, must be acknowledged to have taken the critical first steps.