The work entitled The Importance of Illustrator in Designing a Book is intended to be a review work and takes us into the world of illustration, it teaches us what a picture book and illustration is and what their purpose is. It guides us through the history of picture books in the world and in Croatia, describes the differences and types among picture books. It will explain why a quality picture book is of great importance for the development of children and their reading habits. The process of creating a picture book will be described, what the layout of the elements on the paper should be, what colors fit the particular text, the elaboration of the appearance of the characters, the size and appearance of the text. The international and Croatian awards for children's literature will be presented, according to which the creativity and awards of Croatian illustration authors in the period from 1990 to 2018 were evaluated. Most of the presented ten Croatian authors have been nominated by the Croatian Center for Children's Books and presented at the Children's Book Fair in Bologna, which will be further discussed below. The paper sought to clarify how complex and demanding the creation of a picture book and illustration is during the development of children as independent people with their own opinions and sense of aesthetics.