This chapter delves into the concept and practicalities of transactional databases, which are crucial for managing and analyzing data across various fields. A transactional database consists of an unordered collection of transactions, each comprising a set of items represented in binary form. The chapter begins with a formal definition of transactional databases using set theory, explaining transactions and patterns. It then addresses practical aspects, including how these databases are stored and formatted on computing devices, with specific file creation and management guidelines. The chapter also covers methods for generating synthetic transactional databases for testing and benchmarking purposes, converting structured dataframes into transactional databases, and analyzing database statistics, including transaction length, item frequency, and sparsity. Overall, it provides a comprehensive overview of both theoretical and practical aspects of transactional databases, offering valuable data management and analysis insights.