Encyclopedia of Islam, Encyclopedia of the Qur'an and Encyclopedia of the Modern World of Islam are three important encyclopedias that orientalists have written about Islam in the last one hundred years.
 Because the Westerners are considered to be the originators of writing encyclopedias in today's formats, it is expected that they have followed the standards known in compiling the encyclopedia; including the observance of comprehensiveness in the selection of entries as well as comprehensiveness in the content presented in the articles - which means to address all the basic and important points of view in each subject.
In this research, which is carried out with a descriptive and analytical method and in a library format and referring to the entries and articles of these encyclopedias, it is intended to answer the question that to what extent orientalists have observed the principle of comprehensiveness in Islamic encyclopedias.?
It is clear from this research that the Islamic encyclopedias of Orientalists have not respected the principle of comprehensiveness in a number of fields, especially in the topics, terms and doctrines related to Shia, and for this reason, they have many shortcomings.
The necessity of exploring this topic is because these encyclopedias are the most important source and reference for the introduction of Islam in the West and the result of this research can encourage Muslim thinkers, seminarians and academics to make a new effort in the field of encyclopedia writing, especially in foreign languages. It can lead to the organization of scientific communication with the editors of western encyclopedias and the re-authoring, correction and completion of some articles.