The lexicon is in fact two dictionaries in one: first the entire English text (pp. 1-274), then the French (pp. 275-574). Within the distinct sections, each term in English is followed by the French equivalent and vice versa for easy cross-checking. Viale has chosen two of the five official languages of the United Nations and perhaps the two most important languages in terms of international environmental treaties.
The alphabetical entries are followed by thematic lists (e.g. climate, fauna, flora, pollution, sea, etc.). These thematic lists are important for persons working on a particular subject who want to gets to grip quickly with all the relevant terms of art. Some of these are fairly short (e.g. “bromine” with three entries) and others are extensive (e.g. “pollution” running to nearly 5 pages). Individual terms are included under all the themes to which they pertain, for example, “bluefin tuna” is listed under “fauna,” “fish” and “sea”. Indeed, it is with examples like “bluefin tuna” that the wisdom of including both languages becomes apparent. Bluefin tuna, in French, is known (inexplicably to an Anglophone) as “thon rouge.” No doubt, the French find the English term equally perplexing.
Viale refers only to binding instruments of global scope, i.e. international treaties, not soft-law instruments such as conference declarations, United Nations General Assembly declarations or regional agreements. This guarantees the accuracy of the entries as they are each the product of carefully negotiated and agreed texts binding on multiple state parties and avoids the risks of error, vagueness or overly progressive definitions which might result from relying on non-binding instruments. Viale further avoids colouring any of the entries with his own interpretation or opinion by referring only to the official text. Nevertheless, it is perhaps a little too careful in this regard as it seems strange to bypass completely the historic Stockholm (1972) and Rio (1992) Declarations. Further, even reliance on binding treaty texts is no guarantee that the text is binding on any given state; additional investigation is necessary for anyone using the text in a particular context to determine whether the convention has been ratified by the state in question (thus confirming that state’s endorsement of the definition). This choice of methodology might have been better explained in the introduction.
Viale’s concern for objectivity means that there are no entries for oft-cited but indeterminate terms of questionable legal status such as “precautionary principle.” No universally accepted definition exists in any international, binding text. Terms such as “monitoring”, “notification” and “environmental impact assessment” are also excluded on similar grounds even if, unlike the precautionary principle, there is sufficient international practice, opinio iuris and jurisprudence to consider them elements of customary international law. Still, to attempt to include a definition of such terms would have changed the very nature of the Lexicon by introducing subjectivity and therefore imperilled its authority as a compilation of agreed international terminology.
Lexicon of Environmental Law is a product of meticulous research and will serve well those who work at the coal-face of environmental law, especially those to whom it is explicitly aimed (NGOs, lawyers, diplomats, students). It is impossible to memorise the sea of environmental terminology and undoubtedly useful to have at hand a quick and simple reference guide, rather than having to trawl multiple treaties for definitions and possibly missing some in the process. Law requires precision, even more so, international diplomacy, and this text provides it.
 Stockholm Declaration on the Human Environment (1972) 11 ILM 1416; Rio Declaration on Environment and Development (1992) 31 ILM 876.