The subject of openings in storage tanks and unfired pressure vessels is an established knowledge base developed from a century and a half of experience. Few technical areas related to tank and pressure vessel pressure boundary penetrations (openings) remain not fully understood. Nevertheless, knowledge on the subject is ever evolving. The content of this book is limited to a presentation of storage tank and pressure vessel openings and their importance in vessel design. No new, groundbreaking concepts are revealed; instead, it is felt that this book offers an efficient compilation of practical and relevant information. Some subject matters covered in this book have not been incorporated into the formal curricula of higher education institutions. New practitioners joining the field of vessel design typically gain their knowledge of these topics through work-assigned projects, sometimes with frustrating and less than timely results. This complex subject is broken down into smaller, more digestible subtopics to make the content more accessible. The chapters follow in a logical sequence beginning with the most fundamental aspects of the subject, progressively becoming more relevant, and finishing with the more technically challenging engineering considerations of storage tank and pressure vessel openings. The progression from fundamental to advanced topics enables readers, based on their experience, to navigate quickly to their points of interest. A certain amount of informational duplication has been purposely incorporated to allow the reader the opportunity to study and benefit from individual chapters in a stand-alone fashion.