This thesis titled ”The Application of ESG Principles in Sustainable Business: An Assumption for Long-Term Success in Selected Companies" analyzes the implementation of ESG (Environmental, Social, Governance) principles in business through research that included a survey of 45 respondents educated in the field of ESG and interviews with representatives from three selected companies: Kaufland k.d., Social Cooperative Humana Nova, and Croatian Post d.d. The study examines perceptions and attitudes toward ESG among respondents educated in this area and compares them with the practices and challenges faced by these companies. The aim of the research is to confirm the assumption that the application of ESG principles positively impacts the long-term sustainability of companies. The survey results showed a high level of awareness and support for ESG principles among respondents, with the majority believing that ESG positively influences the long-term success of companies. Respondents recognized the importance of an integrated approach in the application of ESG but also highlighted challenges such as a lack of expertise and financial resources. Despite the high level of support, there is some uncertainty regarding specific aspects of ESG, such as the creation of a positive corporate image with the public and the reduction of operational costs. Interviews with representatives from the selected companies revealed different approaches to ESG implementation, with a focus on environmental initiatives at Kaufland and Croatian Post, and also on social aspects at Humana Nova. All respondents emphasized the importance of a holistic approach and specific challenges they face, such as high initial costs, lack of support from legislative bodies, and the complexity of data collection. Despite these challenges, all three companies recognize the long-term benefits of ESG, including improved corporate reputation, operational efficiency, sustainable growth, and social responsibility.