Data reconciliation is a complex yet essential process in data engineering, aimed at ensuring data accuracy, consistency, and integrity across different systems, which is vital for industries such as finance, healthcare, and telecommunications. This process involves comparing data from multiple sources to maintain its integrity and reliability, which helps prevent errors and discrepancies that can arise from different data formats, entry mistakes, or timing issues. The article is the first in a three-part series that will explore various aspects of data reconciliation, including defining success, use cases in data replication and migration, and the technical challenges involved. It also highlights the importance of data reconciliation in complying with regulations like the Sarbanes-Oxley Act and HIPAA, which mandate accurate and consistent data for legal and financial accountability, as well as patient care. Due to its complexity, many teams resort to manual validation or custom solutions, but effective data reconciliation ensures that transferred data maintains its original function, meaning, and detail without loss or corruption.