This Privat-Docent thesis highlights broad HEE concepts and underpinning issues inherent to HTA. Key elements, such as health outcome measurements, decision-making under intrinsic uncertainty conditions with probabilistic approach, and future challenges regarding cost-effectiveness thresholds and utilitarianism, are discussed in the introduction. In the appendices, a selection of five articles from own research works are presented to exemplify the implementation of health economic studies from clinical trials.