This study examines the influence of social media marketing on customers' purchasing behaviour and decision-making in the modern digital era. Social media platforms such as Instagram, YouTube, and Facebook have become essential tools for businesses to promote products, communicate with consumers, and build strong brand presence. The study is based on both primary data collected through a structured questionnaire and secondary data obtained from books, journals, and reliable online sources, using a descriptive research design. The analysis shows that social media significantly influences customer awareness, perceptions, preferences, and final purchase decisions. Consumers today actively seek information through social media, where factors such as online reviews, advertisements, and influencer recommendations play a vital role in shaping their attitudes and purchase intentions. Moreover, social media platforms provide businesses with opportunities to engage with customers, gather feedback, and personalize marketing strategies. The study also highlights that consistent and effective social media marketing enhances customer trust, strengthens brand loyalty, and improves customer satisfaction. It concludes that social media marketing is a powerful and cost-effective tool that enables businesses to reach a wider audience, influence consumer behaviour, and improve sales performance in a highly competitive market.