It is well-established in reading assessment that items measuring the same reading skills may vary in difficulty, which makes it almost impossible to come to a definite conclusion concerning the hierarchy of those skills. This challenge is primarily due to the influence of item and text characteristics on the difficulty level of an item. These include the item format, context type, question type, explicitness or implicitness of information, text type, syntax, text structure, lexis and text length. Given the critical role that reading plays in literacy development and learning, it is hoped that this research book will provide researchers and practitioners with a better understanding of how reading skills can be tested and how item characteristics can influence the difficulty level of items. It is also hoped that this book will be a helpful reference for researchers interested in using the Many-facets Rasch Model and the FACETS software to investigate the hierarchical ordering of reading or other language skills.