The modular nature of Boundless textbooks means that a given subject has a number of different textbooks in it, each with largely the same content, but in different orders and with some changes to which content modules are included.

This can be understood in terms of Boundless subjects and their division into the Boundless textbook associated with the subject and the alignments created from that textbook.

Boundless Subjects

Boundless content currently covers a wide variety of subject areas (for example, Chemistry, Writing, and World History). 

Each subject has a single official Boundless textbook, alignments to educators' syllabi, and community-contributed books that fall under that subject.

Boundless Subject Textbooks

The Boundless textbook for a given subject (say, Boundless Chemistry) includes all the Boundless-created concepts on that subject, organized into chapters and sections. 

The ordering of the concepts in the book and the titles of the chapters and sections are the distinguishing characteristics of the canonical Boundless version of a subject textbook.

Alignments

The content modules in a Boundless textbook are modular. With our book editor, the content modules of a given subject textbook can be re-organized into different chapters and sections, which can themselves be renamed. Modules can also be removed from the book and added from other subjects.

These customized books are called alignments, because they align to the order of specific educators' syllabi.