Social media has revolutionized business-to-customer communication from the traditional, one-way broadcast selling to two-way relationship-building marketing strategies. From their humble origins as relationship sites for personal contacts, social media sites have grown to become powerful marketing hubs where brands, influencers, and consumers converse using highly evolved, multi-dimensional, multi-directional conversations. This paper reviews recent studies in the area of social media and how they affect online marketing, detailing how they shape consumer behavior, redefine brand communication strategies, and open new possibilities for business growth. On the one hand, social media provide unparalleled access to international audiences and instant interaction with them. On the contrary, it generates issues such as privacy concerns, information overload, and a requirement for genuine brand presence in more skeptical online spaces.