Abstract "Yazid bin Mohammed Al-Bohlawi Al-Sahtani's Essential Grammar Study and Investigation" is the title of this research which includes two sections: (1) the study and (2) the investigated text. Section 1 is divided into two chapters. Chapter 1 speaks about the writer and the book in three parts. Part 1 is a short introduction about the author, Part 2 investigates the title of the book, and Part 3 studies the efforts to determine the real author of the book. Chapter 2 studies the book under four titles as follows: the author's differing grammatical opinions, his resources, the influence of the Kofa School on him, and the book's distinctive phenomenas. A group of poetry lines which the author quotes from Kofi, linguistics, and poetry books are attached to this section as well as poetry which has unknown writers. Also, a response to Sheikh Mohana bin Khalfan Al-Kharosi regarding the real author of the book is provided. As for Section 2, it includes the investigated text Essential Grammar. The book discusses grammatical issues by dividing them into 115 sections. Throughout the book, the author tries to avoid complexities and quotations but provides ample evidence. Illustrative appendices are attached at the end of the paper.