Although there are a lot of modalities that can measure the mandible linearly, there are no clear studies done to test the accuracy of each method. Therefore studying of the Characteristics and reliability of length measurements of the human mandible by comparing orthopantomograms (OPTs) and lateral cephalogram will give the answers about the raised questions about the accuracy of these two methods. This Book fall into five chapters, Chapter one consists of introduction about the OPT and Cephalogram, objectives, significant of the study and the overview of the study. Chapter two includes the literature review, Chapter three detailed the material and methods, Chapter four includes the presentation of the results, and finally chapter five include the discussions, conclusion, recommendation and summary.