The article presents the key stages of conducting ESG due diligence, along with a list of questions that can be used to assess a company’s level of maturity in sustainable development management across individual stages of mergers and acquisitions (M&A). The article analyses the legal requirements for incorporating ESG issues into M&A processes, especially regarding the identification, assessment, and disclosure of sustainability-related risks and opportunities. It also provides a comprehensive review of the academic literature on due diligence in both transactional and ESG contexts. Furthermore, the article explores the integration of ESG due diligence into the transactional process. The article may be particularly useful for M&A practitioners facing the challenges of effectively embedding ESG aspects into their ongoing processes.