Books can be treatises or textbooks. Both are academic, scholarly works that offer contextual discussion of the law on a particular topic. They offer analysis and interpretation assistance and point to useful case authorities.
Treatises are thorough expositions of an area of law and often have gone through numerous editions. They are heavily footnoted with leading cases and other scholarly works.
Textbooks are also scholarly but are often offer a less in-depth discussion with fewer footnotes. They also may be in an early edition, so their authoritativeness is not yet established.
For a more thorough description of treatises and textbooks, go to the Legal Research and Writing Libguide.