Companies in the EU face increasing challenges and pressures, especially with regulatory requirements like CSRD demanding significant responses. Integrating sustainability through strategic CSR can effectively embed sustainable practices into core operations. This study provides a rare integrative understanding by considering industry, resource, and stakeholder perspectives. Semi-structured interviews with employees in sustainability roles for 1-2 years in SMEs and large EU companies reveal internal and external drivers pushing companies towards sustainability, highlighting whether they adopt a proactive or reactive stance. Findings indicate that external drivers, such as regulatory mandates and stakeholder expectations, are significant catalysts for sustainability, emphasizing the importance of compliance and reputation. Internally, resource allocation and organizational culture are crucial, balancing financial considerations and fostering a sustainability-oriented mindset among employees. Companies with a stronger sustainable culture perceive internal drivers as more influential, aligning with a proactive CSR strategy. Additionally, the study highlights the critical role of stakeholder engagement in driving effective sustainability strategies. Companies that actively engage stakeholders and prioritize their needs demonstrate a higher commitment to sustainability, leading to enhanced reputational benefits and long-term value creation.