An engineering notebook is a bound book that contains the ideas of its author, along with all notes, data, observations, calculations, and other information relevant to the discovery or experiment being conducted. It provides an important record of an engineer or inventor's work. When properly maintained, it may be submitted as a legal document for patent purposes or legal records.

The purpose of an engineering notebook is to offer a time-sequential written documentation of the efforts of its author on a project. It is the equivalent of a technical diary and has many functions. It consolidates data for easy access, allowing an author to confirm conclusions, details, or dates. It can reveal previous trends and can provide useful information for estimating the time or effort required on future projects. It may also offer memory refreshment on points of fact or paths of inquiry that have been investigated, and can offer justification for decisions or courses of action.

There are key points of information an engineering notebook should contain to document a history of work as evidence. All data should be recorded directly into the notebook in chronological order, including notes and calculations with as many details as possible. For experiments and inventions, explicit details and dates of an idea's origin must be included, along with specifics about the development process and ways in which discoveries were made. How a project or invention operates, experimentation observations, results, and other details should also be recorded. Significant events may be corroborated by a non-inventor colleague who witnesses the work that is done, and then signs a "Disclosed to and Understood by" clause on relevant pages.

How information is recorded in an engineering notebook is just as important as the data included. Only an attorney can supply legal instructions, but scientifically accepted guidelines dictate that an engineering notebook must be bound and pages should be numbered to ensure continuity. All entries should be made in permanent ink by the author, and should be signed and dated clearly. No blank pages or spaces should be kept and pages should never be removed; errors can be struck through with a single line, and a small, dated notation should refer to a page where the correction is located. If necessary, items may be taped into the notebook with a handwritten date and title.