Modern slavery and human rights are social sustainability issues. Under the triple bottom line (environmental, social, economic), the social dimension covers labour rights, working conditions, equality, and compliance with modern slavery laws. Responsible sourcing requires buyers to integrate such social criteria in supplier prequalification to prevent unethical practices from entering supply chains. Environmental criteria cover impacts like carbon and waste; economic focuses on cost and competitiveness; quality addresses technical performance. Including modern slavery checks at the prequalification stage reflects due diligence and ensures alignment with legal and ethical obligations.