This report provides an in-depth examination of the requirements for creating and substantiating verifiable sustainability claims within the regulatory framework of the European Green Deal. It focuses on the EU Commission's proposed Green Claims Directive, alongside related legislative initiatives such as the Corporate Sustainability Reporting Directive (CSRD) and the European Sustainability Reporting Standards (ESRS). These frameworks collectively aim to combat greenwashing and ensure that sustainability claims are factual, transparent, and credible. The report refers to a "verifiable sustainability claim" as one that is both correct and formulated in a way that it can be evaluated against objective, standardized criteria. It presents practical methodologies and tools, including checklists, to assess whether a claim is verifiable and whether a claim would comply with the current proposal of the EU Commission’s Green Claims Directive. To ensure relevance and practical guidance, real cases of sustainability statements and claims are studied at the participating process industry companies, regarding how to interpret, express, and set requirements for verifiability and substantiation of sustainability claims. This report also includes an extensive literature study presenting relevant directives, standards and other literature relevant to the subject of sustainability claims and green claims. The study extends beyond consumer-focused claims to explore implications for business-to-business communication and reporting. By integrating insights from international standards (e.g., ISO 14020, ISO 14067), certification systems (e.g., Nordic Swan, ISCC), and methodologies for lifecycle assessments and environmental product declarations (EPDs), the paper provides actionable guidance. Recommendations emphasize avoiding vague, misleading, or irrelevant claims and adopting structured approaches to ensure precision and compliance. In addition, this report, developed under the Climate-leading Process Industry initiative, not only supports industries in fulfilling regulatory obligations but also enables them to establish credibility and trust. It aligns with the EU’s broader climate objectives, including the “Fit for 55” initiative, aiming to reduce emissions by 55% by 2030 and achieve climate neutrality by 2050.