For many years the idea that for high information processing systems effectiveness, high quality of data is not less important than the systems’ technological perfection was not widely understood and accepted. The way to understanding the complexity of the data quality notion was also long, as will be shown in this paper. However, progress in modern information processing systems development is not possible without improvement of data quality assessment and control methods. Data quality is closely connected both with data form and value of information carried by the data. High-quality data can be understood as data having an appropriate form and containing valuable information. Therefore, at least two aspects of data are reflected in this notion: (1) technical facility of data processing and (2) usefulness of information supplied by the data in education, science, decision making, etc.