In this thesis, the concepts of complexity and how the influence of complexity affects product quality are described and explained. The initial metrics of complexity, structural complexity, control flow complexity are presented and the importance of data quality in the mentioned area is explained. The types of complexity are described in detail, their origin, and where they can be used. Those claims are supported by the evidence of various formulas that are related and derived from them. Structural metrics, their differences, and their implementation were defined. The quality, development, and processes that start from the idea all the way to the implementation of the software product are presented. After that, the role of complexity on software quality, the ways in which it can change very quickly, the most common culprits that can cause it, and the importance of refactoring and writing good and clean code, in order to reduce the possible technical accumulated debt in the future alongside with maintenance of software were discussed. The story is rounded off with a modern theme that was based on quality assurance in artificially intelligent systems and the ways in which complexity can be measured against traditional software systems.